INFORMATION TO USERS
This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer.
The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely afreet reproduction.
In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.
Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book.
Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order.
University Microfilms International A Bell & Howell Information Company 3 0 0 North Z eeb Road, Ann Arbor, Ml 4 8 1 06-1346 USA 313/761-4700 800/521-0600
Order Number 9130509
Allozyme variation and evolution inPolygonella (Polygonaceae)
Lewis, Paul Ollin, Ph.D. The Ohio State University, 1991
Copyright ©1991 by Lewis, Paul Ollin. All rights reserved.
UMI 300 N. Zeeb Rd. Ann Aibor, MI 48106
ALLOZYME VARIATION AND EVOLUTION IN POLYGONELLA
(POLYGONACEAE)
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy in the Graduate
School of The Ohio State University
By
Paul O llin Lewis, B.A., M.Sc.
*****
The Ohio State University
1991
Dissertation Committee: Approved by:
Dr. Daniel J. Crawford
Dr. Allison A. Snow Advisor
Dr. Tod F. Stuessy Department of Plant Biology Copyright by Paul Ollin Lewis 1991 To my parents, Joe and Shirley Lewis ACKNOWLEDGMENTS
I would like to express appreciation to my advisor, Dr. Daniel J. Crawford, and the other members of my committee, Drs. Allison A. Snow and Tod F. Stuessy, for their encouragement and suggestions. Thanks go also to Drs. Gary L. Floyd and Morris Cline for participating as members of my General Examination
Committee. I would especially like to thank all those at the Archbold Biological
Station, Lake Placid, Florida, for their kindness and helpfulness in this project.
The following persons served me by engaging me in very productive discussions about biogeography, endemism in Florida, and other topics related to this project: Dr. Steven P. Christman, Dr. Mark Deyrup, David Haines, Dr. Walter S.
Judd, Dr. Eric S. Menges, Susan Wallace, and Dr. Richard P. Wunderlin. Dr. Guy
L. Nesom has been a source of continuous encouragement and first introduced me to the interesting genus Polygonella. I would especially like to thank my wife and best friend LuAnn, for her encouragement, love, and understanding, and my parents for their unconditional and neverending love and support of my endeavors. VITA
December 29, 1961 ...... Born, Louisville, Kentucky
1982 ...... B.A., Biology and Mathematics, Georgetown College, Georgetown, Kentucky
1984 ...... M.Sc., Biology, Memphis State University, Memphis, Tennessee
1988 ...... Doctoral Dissertation Improvement Grant, National Science Foundation
PUBLICATIONS
1983. Browne, E. T., Jr., K. Broyles and P. Lewis. Trianthema portulacastrum L. (Aizoaceae) in Tennessee. Castanea 48: 238.
1984. Bates, V., and P. Lewis. Rediscovery of Stylisma humistrata (Convolvulaceae) in Tennessee. Rhodora 86: 393-394.
1984. Lewis, P., and G. Nesom. Label writing program in MBasic for microcomputers. Herbarium News (Missouri Bot. Gard.) 4(2): 6-7.
1985. Bates, V., L. M. Wilson and P. Lewis. Notes and new distributional records for several Tennessee orchids. J. Tennessee Acad. Sci. 60: 45-48.
1989. Lewis, P., and R. Whitkus. GENESTAT for microcomputers. ASPT Newsletter 2: 15-16.
1990. Lewis, P. PeaStats: a computer program for use with introductory Plant Biology courses. Plant Science Bulletin 36: 8.
1991. Lewis, P., and E. T. Browne, Jr. The vascular flora of Haywood County, Tennessee. J. Tennessee Acad. Sci. 66: 37-44. 1991. Lewis, P. Allozyme variation in the rare Gulf Coast endemic Polygonella macrophylla Small (Polygonaceae). In press: Plant Species Biology.
FIELDS OF STUDY
Major Field: Plant Biology
Studies in plant systematics and evolution, Dr. Daniel J. Crawford, Advisor. TABLE OF CONTENTS
DEDICATION...... ii
ACKNOWLEDGEMENTS ...... iii
VITA ...... iv
LIST OF TABLES ...... viii
LIST OF FIGURES ...... x
LIST OF PLATES ...... xiii
INTRODUCTION ...... 1
CHAPTER PAGE
I. CLADISTIC ANALYSIS OF POLYGONELLA AND ITS RELATIONSHIP TO POLYGONUM SUBG. DURAVIA ...... 35
Introduction ...... 35 Materials and Methods ...... 39 R e su lts ...... 45 D iscussion ...... 47 Summary ...... 54 Literature Cited ...... 56
II. ALLOZYME VARIATION IN THE RARE GULF COAST ENDEMIC POLYGONELLA MACROPHYLLA SMALL (POLYGONACEAE) ...... 80
Introduction ...... 80 Materials and Methods ...... 82 R esu lts ...... 85 D iscussion ...... 87 Summary ...... 93 Literature Cited ...... 94 III. ALLOZYME VARIATION IN THE GENUS POLYGONELLA: COMPARISON WITH OTHER SEED PLANTS...... 105
Introduction ...... 105 Materials and Methods ...... 106 Results and Discussion ...... 113 Summary ...... 128 Literature Cited ...... 130
IV. CORRELATION OF GENE DIVERSITY WITH LATITUDE IN POLYGONELLA (POLYGONACEAE): TESTING AN HYPOTHESIS INVOLVING HISTORICAL FACTORS ...... 156
Introduction ...... 156 Materials and Methods ...... 160 R esu lts ...... 165 D iscussion ...... 166 Summary ...... 173 Literature Cited ...... 175
APPENDICES
A. POLYGONELLA LOCALITIES VISITED DURING THE COURSE OF THIS STUDY...... 188
B. NEXUS DATA SET USED IN CHAPTER I ...... 206
LIST OF REFERENCES...... 211 LIST OF TABLES
TABLE PAGE
1. Characters and character states used in the cladistic analyses of Polygonella and Polygonum subg. Duravia ...... 58
2. Abbreviations used in the text, number of individuals sampled from each population (average sample size over all loci), and collection locality descriptions. Voucher specimen citations are italicized at the end of the locality descriptions ...... 96
3. Estimated allele frequencies for 10 loci among six populations of Polygonella macrophylla. Numbers of heterozygotes (G) and sample sizes (N) for each locus and population are indicated above the frequencies in the following format: G / N. Missing data are indicated by hyphens (—) ...... 97
4. Sample proportion of polymorphic loci (P), mean sample number of alleles per polymorphic locus ( Ap), mean sample number of alleles per locus (A), sample gene diversity (ff ), unbiased for sample size following Nei (1987), sample observed heterozygosity (H ) and number of unique alleles detected in populations and color classes in the species Polygonella macrophylla ...... 98
5. Mean values for total sample gene diversity (//T), sample gene diversity within populations (//s), sample gene diversity among populations (f>ST), and sample coefficient of differentiation among populations (CST) for all loci among populations in the "rubra" and "alba" color classes of Polygonella macrophylla. All four estimates were calculated using equations 9 and 11 of Nei and Chesser (1983) to correct for sample size ...... 99
Above the diagonal: Geographical distances among the six populations of Polygonella macrophylla in kilometers taken as the shortest route following the Gulf Coast. Below the diagonal: Sample genetic distance (£>) values for pairwise comparisons of the six populations. Marginal values are mean distances from individual
viii populations to the other five populations. The negative correlation (r = -0.279) between D and geographic distance is not significant (p > 0.05) ...... 100
7. Estimates of the inbreeding coefficient FjS, which measures the correlation of genes within individuals within populations, using equation 1 of Weir and Cockerham (1984) for the polymorphic loci in Polygonella macrophylla. Significance levels of p < 0.05 are labeled with one (p < 0.05) or two (p < 0.001) asterisks (*); levels greater than p = 0.05 are not labeled ...... 101
8. Estimated rates of gene flow ( Nm) among populations of Polygonella macrophylla from two different methods, Wright’s Fay and Slatkin’s private allele methods. For Wright’s (1951) FSy method, gene flow was estimated as Nm = [(1/FST) - l]/4 by substituting CST or O as estimators of FST. The CST used was unbiased for sample size following Nei and Chesser (1983) and O was unbiased for both sample size and population number following Weir and Cockerham (1984). Both were averaged across loci. For Slatkin’s private alleles method, gene flow was estimated as Nm = exp10([Iog10(p(l)) + 1.1]/ - 0.58} following the values recommended for a sample size of 25 by Slatkin and Barton (1989) ...... 102
9. Population name, state, county, number of loci sampled (L), and mean number of individuals sampled per locus (N) in the following format: Name (S t a t e : County) [L , N] ...... 133
10. Sample sizes and gene diversity statistics for the eleven species of Polygonella ...... 135
11. Data set for 74 populations comprising 11 species® (SPP) scored for unbiased gene diversity (//), and latitude (LAT) ...... 179
12. Mean values for each species for total gene diversity HT, within population gene diversity Hs, and latitude ...... 181
13. Examples of species and congeneric species pairs that could provide valuable insight into the effect on gene diversity of large-scale northward plant migration following the Wisconsin glaciation in North America ...... 182
ix LIST OF FIGURES
FIGURE PAGE
1. Geographic distribution of Polygonella fimbriata (•) in Georgia, U.S.A., and P. robusta (■) in Florida, U.S.A ...... 15
2. Geographic distribution of Polygonella articulata in Illinois, Indiana, Iowa, Michigan, Minnesota, and Wisconsin, U.S.A., and southern Ontario, Canada ...... 17
3. Geographic distribution of Polygonella articulata in the northeastern United States and Quebec, Canada ...... 19
4. Geographic distribution of Polygonella parksii in Texas, U.S.A ...... 21
5. Geographic distribution of Polygonella americana in the southeastern United States ...... 23
6. Geographic distribution of Polygonella myriophylla in Florida, U.S.A...... 25
7. Geographic distribution of Polygonella macrophylla in Alabama and Florida, U.S.A ...... 27
8. Geographic distribution of Polygonella polygama var. polygama (•), P. polygama var. croomii (■), and P. polygama var. brachystachya (4) in the southeastern United States ...... 29
9. Geographic distribution of Polygonella gracilis in Alabama, Florida, Georgia, and South Carolina, U.S.A ...... 31
10. Geographic distribution of Polygonella ciliata (•) and P. basiramia (■) in Florida, U.S.A ...... 33
11. Illustration of possible relationships between Polygonella and Duravia 60
12. Illustration of the use of constraints in phylogenetic analysis. A. Consensus tree used as a constraint. B. Resolutions permitted under constraint ...... 62
x 13. The distribution of tree lengths resulting from an exhaustive search of all possible topologies ...... 64
14. Consensus trees for Polygonella subg. Duravia. A . Semistrict consensus of the four most-parsimonious trees. B. Semistrict consensus tree (rooted) of the 36 trees of length 37 or less ...... 66
13. Semistrict consensus tree based on 340 equally most-parsimonious trees from an heuristic search of all taxa ...... 68
16. Consensus tree for Polygonella showing distribution of chromosome num bers ...... 70
17. Cladogram for Polygonella showing (bold lines) lineages leading to perennial species ...... 72
18. Cladogram for Polygonella showing distribution of breeding systems; species not labeled are gynodioecious ...... 74
19. Cladogram for Polygonella showing the relative extent of geographic distribution for each species ...... 76
20. Map of western Florida and southern Alabama (U.S.A.) showing locations of populations of Polygonella macrophylla sampled for this study. Populations of "rubra" are labeled RB (Royal Bluff) and RD (Royal Dune). Populations of "alba" are labeled GS (Gulf Shores), D (Destin), GB (Grayton Beach), and PC (Panama City). That part of North America shown in detail is indicated on the inset map of North America ...... 103
21. Total (H„) and intrapopulational (Hg) gene diversity and coefficient of gene differentiation (CST) in Polygonella compared to seed plants ...... 136
22. Total gene diversity (HT) in Polygonella compared to seed plants, classified by life span ...... 138
23. Gene diversity within populations (Hg) in Polygonella compared to seed plants, classified by life span ...... 140
24. Coefficient of gene differentiation (CgT) in Polygonella compared to seed plants, classified by life span ...... 142
25. Total gene diversity (HT) in Polygonella compared to seed plants, classified by breeding system ...... 144
26. Gene diversity within populations (Hg) in Polygonella compared to seed plants, classified by breeding system ...... 146
xi 27. Coefficient of gene differentiation (CST) in Polygonella compared to seed plants, classified by breeding system ...... 148
28. Total gene diversity (HT) in Polygonella compared to seed plants, classified by extent of geographic distribution ...... 150
29. Gene diversity within populations (Hg) in Polygonella compared to seed plants, classified by extent of geographic distribution ...... 152
30. Coefficient of gene differentiation (CgT) in Polygonella compared to seed plants, classified by extent of geographic distribution ...... 154
31. Scatter plots of gene diversity (ordinate) against mean latitude (abscissa) for the eleven species of Polygonella. A . Total gene diversity, HT, unbiased for both sample size and number of populations sampled. B. Within-population gene diversity, Hg, unbiased for sample size ...... 154
32. Scatter plot of gene diversity, H, unbiased for sample size, (ordinate) against latitude (abscissa) for the eleven populations of Polygonella gracilis ...... 154
33. ANOVA tables and standardized regression coefficients for total gene diversity (HT) and gene diversity within populations (Hg) for regressions of gene diversity on the traits breeding system, life span, geographic distribution, and mean latitude in Polygonella ...... 154
xii LIST OF PLATES
PLATE PAGE
I. Comparison of scanning electron micrographs of pollen from selected representatives of three major subgroups of Polygonum and Polygonella. Scale bar is 5 urn. 1. Polygonum aviculare L. [Lewis 2141 (OS)]. 2. Polygonum pensylvanicum L. [Taylor-Lehman, no number (OS)]. 3. Polygonum paronychia Cham. & Schlecht. [Sundberg 2011 (TEX)]. 4. Polygonum californicum Meisn. [Arnaud, Jr., 19-Oct-1968 (TEX)]. 5. Polygonella robusta (Small) Nesom & Bates [Bozeman 11334 (SMU)]. 6. Polygonella fimbriata (Ell.) Horton [Hardin & Duncan 14328 (GA)] ...... 79 INTRODUCTION
Polygonella (Polygonaceae) is a North American flowering plant genus of eleven species, distributed from southern Ontario south to Florida and Texas, and from Maine west to New Mexico (Figures 1 to 10). All but one species (P. articulata) are distributed south of 37° N latitude, and peninsular Florida is the area of greatest overlap in species’ distributions. Only four of the eleven species have no populations in Florida ( P. americana, P. articulata, P. fimbriata, and P. parksii) and five species are endemic (or very nearly endemic) to that state (P. basiramia, P. ciliata, P. robusta, P. macrophylla, P. myriophylla).
V a r ia t io n in E c o l o g ic a l a n d L if e H is t o r y T r a it s
There is considerable variation among the Polygonella species in traits such as life span (annuals, perennials), geographic distribution (widespread, restricted), breeding system (hermaphroditic, gynomonoecious, gynodioecious, dioecious), chromosome number (n = 11, 12, 14, 16, 18), and habit (erect, prostrate). The relationship of traits such as these to the amount of allozyme variation maintained within populations and species is specifically addressed in
Chapter IV.
Six species are annuals ( Polygonella articulata, P. basiramia, P. ciliata, P. fimbriata, P. gracilis, P. parksii) and the remaining five ( P. americana, P. macrophylla, P. myriophylla, P. polygama, P. robusta) are perennials of uncertain
1 2 average life span. I have seen indications in the field {e.g., dead branches apparently from the previous year) that individuals of some of those species listed among the annuals may live for more than one year if the climate is favorable, and, conversely, many of the perennials would doubtless behave as annuals if their ranges were further north (the northernmost species, P. articulata, is an annual). The only perennial to have populations both in peninsular Florida as well as in North Carolina has much higher fecundity in
Carolina populations than in Florida populations; selection for greater fecundity probably accompanied the shortening of the life span (these northern plants have no underground perennating structures and are probably killed by the periodic hard freezes that occur in North Carolina).
Six species are quite narrowly restricted geographically [Polygonella fimbriata (endemic to Georgia), P. parksii (endemic to Texas), P. myriophylla
(endemic to the Lake Wales Ridge in peninsular Florida), P. macrophylla
(endemic to the Gulf Coast of the Florida panhandle and Baldwin Co.,
Alabama), P. ciliata (endemic to Florida), and P. basiramia (endemic to the Lake
Wales Ridge in peninsular Florida)], four are relatively widespread [P. articulata
(Great Lakes region, New England, northern east coast of North America), P. americana (Carolinas west to New Mexico), P. polygama (southeastern U.S.), P. gracilis (southeastern U.S.)], and one is intermediate [P. robusta (Florida peninsula)] in extent of geographic distribution. This disparity in distribution size is a function of both dispersal ability and habitat specificity. It is not surprising that some species are not widespread; e.g., P. myriophylla, which has no obvious dispersal system and is restricted ecologically to a peculiar habitat that is itself endemic to Florida. It is likewise not surprising that P. articulata is one of the most widespread of Polygonella species, as it has a very good wind 3 dispersal system and is tolerant of a variety of native habitats as well as roadsides and other "waste places." Other species that are narrowly restricted endemics have a relatively good dispersal system but are restricted because of an inability to survive in habitats surrounding that to which they have become adapted. Two good examples of this type of species are P. parksii and P. basiramia, both of which are very weedy in their respective habitats, but are not able to survive at all in other similar habitats. The last type of species is exemplified by P. americana, which has apparently a very poor dispersal system but is able to grow in a variety of habitats. It is found at elevations from near sea level to well over a thousand meters, in deep sand to soilless rock outcroppings, and from humid Georgia to xeric New Mexico. In this case, it may be that dispersal was aided by especially strong winds (such as those at the close of the last glaciation) and this species was able to survive better than other species when dispersed into new localities.
Hermaphroditism in plant species (the way I have used it throughout this work) pertains when all flowers of every plant in a population are bisexual, producing male gametes in specialized male reproductive organs
(stamens) and female gametes in specialized female reproductive organs
(carpels). Gvnomonoecv is a departure from hermaphrodity that involves the production of some unisexual, female flowers by every individual in the population. Diclinv involves more drastic departures from hermaphrodity in which two (or more) different types of individuals exist within a population: gvnodioecv involves maintaining some completely female individuals within a population that is otherwise hermaphroditic; and dioecv involves separation of all individuals into two sexes, either male or female. These definitions follow
Richards (1986:285), with exception that I prefer a stricter definition of 4 hermaphrodity that does not include gynomonoecy or monoecy. Three species have hermaphroditic breeding systems ( Polygonella articulata, P. americana, and
P. myriophylla), while the remaining species are diclinous to some degree: P. fimbriata and P. robusta are gynomonoecious; P. parksii, P. macrophylla, P. ciliata, and P. basiramia are gynodioecious; and P. polygama and P. gracilis are dioecious.
H a b it a t
All species of Polygonella inhabit sandy places and avoid habitats in which there is much competition from other plants. There is some variability in the degree of habitat specificity, however. Polygonella articulata, P. gracilis,
P. polygama (especially var. croomii), and to a lesser extent, P. americana and P. robusta, are the species most likely to be found in non-native sandy or gravely habitats, such as open roadsides or recent clearcuts where sandy soil predominates. All of these species, however, may be found as well in native habitats, sometimes alongside those other Polygonella species that are very specific in their habitat preferences. The species that are most restricted ecologically include most of the narrow endemics; the most conspicuous examples are: P. parksii, found only on the Carizzo Sand Formation where it outcrops in Texas; P. myriophylla and P. basiramia, found only in the Sand Pine
Scrub ecosystem, which is itself endemic to Florida; and P. macrophylla, which occupies a narrow strip of Gulf of Mexico coastline only about 50 m in width along the Florida panhandle. The following discussion will concentrate on those natural plant associations in the southeastern United States within which one is most likely to find Polygonella species. The two predominant 5 southeastern United States plant associations occurring on sandy soils are Scrub and High Pine.
Scrub
Scrub vegetation was defined by Myers (1990) as a . xeromorphic shrub community dominated by a layer of evergreen, or nearly evergreen, oaks
(Quercus geminata, Q. myrtifolia, Q. inopina, Q. chapmanii) or Florida Rosemary
(Ceratiola ericoides), or both, with or without a pine overstory, occupying well- drained, infertile, sandy soils." The pine most characteristic of scrub vegetation is the Sand Pine ( Pinus clausa), which is endemic to Florida except for a lobe of its distribution extending west from the panhandle into coastal Baldwin Co.,
Alabama (Laessle 1958; Myers 1990); this particular type of scrub vegetation I will hereafter refer to as Sand Pine Scrub. Slash Pine (P. elliottii) is a less frequent component of scrub vegetation and scrubs of this type are often referred to as Slash Pine Scrubs (Myers 1990). The most frequent and abundant species (besides the pines) making up the Scrub vegetation in Florida are Myrtle
Oak (Quercus myrtifolia), Scrub Oak (Q. inopina), Saw Palmetto ( Serenoa repens) and the related Scrub Palmetto S. etonia, Sand Live Oak ( Q. geminata),
Chapman’s Oak (Q. chapmanii), Rusty Lyonia ( Lyonia ferruginea) and the
Florida Rosemary ( Ceratiola ericoides) (Laessle 1958; Abrahamson et al. 1984a;
Myers 1990).
The particular type of Scrub inhabiting the area known as the Lake
Wales Ridge in central, peninsular Florida is dominated by Sand Pine and harbors a long list of endemic species of plants, including the following: Pigmy
Fringe Tree ( Chionanthus pygmaeus), Scrub Plum (Prunus geniculata), Garrett’s
Ziziphus (Ziziphus celata), Highlands Scrub Hypericum ( Hypericum cumulicola), 6
Scrub Balm (Dicerandra frutescens) and its recently described relative
Dicerandra christmanii, Wedge-leaved Snakeroot ( Eryngium cuneifolium) Beckner’s
Lupine ( Lupinus aridorum), Carter’s Warea (Warea carteri), Florida Gay feather
(Liatris ohlingerae), Shortleaved Rosemary ( Conradina brevifolia), Paper-like
Nailwort ( Paronychia chartacea), Britton’s Bear Grass ( Nolina brittoniana), and, last but not least, the two Polygonella species P. myriophylla (known locally as
Sand Lace) and P. basiramia (Woody Wireweed or H airy Jointweed) (Laessle
1958; James 1961; Zona & Judd 1986; Huck et al. 1989; Myers 1990). Species that are endemic to Scrub but are often present at lower frequencies include
Scrub Holly ( Ilex opaca var. arenicola), Garberia (Garberia heterophylla)
Palafoxia ( Palafoxia feayi), Wild Olive ( Osmanthus megacar pa), Curtiss’
Milkweed ( Asclepias curtissii), Scrub Hickory ( Carya floridana), and Scrub Oak
(Quercus inopina) (Abrahamson 1984a; Myers 1990; Johnson & Abrahamson
1982).
Taxa endemic to the Sand Pine Scrub along the Gulf Coast in the panhandle of Florida and southernmost Alabama are fewer in number; among them are Godfrey’s Blazing Star (Liatris provincialis), Conradina canescens,
Polygonella macrophylla (Large-leaved Jointweed), and the open-coned variety of the Sand Pine, Pinus clausa var. immuginata, the distinctness o f which is currently under debate (Myers 1990). In addition to the three Polygonella species mentioned above, P. ciliata is also restricted to Scrub, both in coastal
Scrubs near Tampa and the Miami area, and in the central part of the peninsula southwest of Orlando. Three Polygonella species (P. robusta, P. polygama, and P. gracilis), while not restricted to scrub vegetation, do not hesitate to grow there. 7
High Pine
The High Pine ecosystem in presettlement times covered a much greater expanse in what is now the southeastern U.S. than at present: a nearly continuous distribution from southeastern Virginia to eastern Texas (Myers
1990). There are two major types of High Pine, Sandhill and Clayhill; as the former is most important for Polygonella species, I will restrict the discussion to
Sandhill vegetation.
The definition given by Myers (1990) for High Pine is the following:
"High pine is an upland savanna-like ecosystem typified by an open overstory of longleaf pine and a ground cover of perennial grasses (primarily wiregrass) and forbs interspersed with deciduous oaks." While Longleaf Pine ( Pinus palustris) is generally the dominant canopy species in Sandhill vegetation, it is often accompanied by deciduous oaks such as Turkey Oak ( Quercus laevis) or
Bluejack Oak (Q. incana), either of which may be present alone or codominant with the other (Myers 1990).
A variety of Sandhill vegetation called Southern Ridge Sandhill is found on the Lake Wales Ridge in central Florida. In this association, South Florida
Slash Pine (Pinus elliottii var. densa) takes the place of Longleaf Pine and a couple of typical inland scrub species are often present, Florida Hickory ( Carya floridana) and Scrub Palmetto ( Sabal etonia) (Abrahamson 1984a; Abrahamson et al. 1984). Other oaks that may or may not be present include Blackjack Oak ( Q. marilandica), Southern Red Oak ( Q. falcata), and occasionally Sand Post Oak ( Q. stellata var. margaretta) (Laessle 1958; Myers 1990). Longleaf Pine has, however, been extensively utilized for its commercial value and, as a result of its exploitation, many areas formerly dominated by Longleaf Pine are now dominated by Turkey Oak. Myers (1990) prefers to refer to these 8 anthropogenic ecosystems as Turkey Oak Sandhills to distinguish them from the original vegetation. The "wiregrass" is usually Aristida stricta but also present and vegetatively indistinguishable from Aristida stricta are Sporobolus junceus and Muhlenbergia capillaris. Other plants in the ground cover include Bracken
Fern (Pteridium aquilinum), Gopher Apple (Licania michauxii), Running Oak
(Quercus pumila), Dwarf Live Oak (Q. minima ), Bluestems (Andropogon spp.),
Golden Aster ( Pityopsis graminifolia), Low-Bush Blueberry (Vaccinium myrsinites), Blackberrry (Rubus cuneifolius), Green Eyes (Berlandiera subacaulis),
Summer Farewell (Petalostemum pinnatum), Splitbeard Bluestem ( Andropogon ternarius), Honeycomb Head ( Balduina angustifolia), Blazing Star ( Liatris pauciflora), Croton argyranthemus, Clammey Weed ( Polanisia tenuifolia), Gopher
Apples (Chrysobalanus oblongifolius), and Dog Tongue ( Eriogonum tomentosum)
(Laessle 1942, 1958; Myers 1990). Species endemic to the High Pine ecosystem are few, among them Clasping Warea (Warea amplexifolia), Pigeon Wing ( Clitoria fragrans), Bent Golden Aster ( Pityopsis flexuosa) and Toothed Savory
(Calamintha dentata) (Myers 1990).
Pvrosenic Nature of Scrub and High Pine Ecosystems
Workers have long been curious as to how and why Sandhill vegetation can predominate in one area and the vegetation of a contiguous area only meters away is pure Sand Pine Scrub. Early investigators were amazed at the bare zone of sand that could be seen separating the two vegetation types (Fig. 2 in Laessle 1958 is a photograph of such a bare zone), but were at a loss to find any differences in the soils from the two areas that were significant enough to explain the segregation (Whitney 1896; Laessle 1958). Initially, some assumed that the two vegetation types had a serai relationship, and there was much 9 debate as to which type gave way to the other (e.g., K urz 1942; Miller 1950), while others insisted that there was no such relationship between the two
(Laessle 1942).
It has come to be understood that these are both pyrogenic ecosystems and fire frequency and intensity are the factors most important in determining the species composition at a particular site (Myers 1985, 1990; Myers & White
1987). The Florida peninsula has 70 to 90 thunderstorm days per year, the highest frequency for any place of comparable size in the nation, and one area of Scrub that has been studies intensively (Archbold Biological Station) averages 10-12 lightning strikes per square km per year, mostly between June and September (Abrahamson 1984a).
The fire regimes and the species responses to fire are quite different between Scrub and Sandhill. Scrub vegetation burns relatively infrequently under natural conditions (once every 30 to 70 years; Abrahamson 1984a), but when it does burn, the fires are very intense and nearly all plant life is killed by the heat of the blaze (Myers 1985). Sandhill, on the other hand, burns frequently (once or even twice per year) but the fires are of such low intensity
(basically ground fires that consume only the grasses) that few if any of the individuals of dominant species such as the deciduous oaks or Longleaf Pine are killed (Abrahamson 1984b; Myers 1985). Species making up Scrub vegetation are described as being fire-resilient, meaning that they regenerate profusely after a fire, whereas Sandhill species are termed fire-resistant, meaning that they resist being killed by the fire (Abrahamson 1984b; Myers
1990). The main circumstance under which Scrub is able to overtake Sandhill vegetation is when fire is excluded (by humans) for a long period of time. This allows fuel to accumulate so that when a fire does occur, perhaps by lightning, 10 the result is devastating to the Sandhill species. Scrub species, if present nearby, can then easily invade a Sandhill area that has suffered a major fire of great intensity (Myers 1990).
P r e v io u s W o r k
The taxonomy of Polygonella was well worked out by Horton (1963) and thus the following is not intended to be more than a brief synopsis of the taxonomic history of this group. Linneus described the first species of the group that later would come to be called Polygonella in 1733. The genus name
Polygonella did not originate until half a century later, in 1803. What follows is an annotated list of the most important events (in chronological order) relating to the taxonomy of this genus from Linneus’ time to the present:
1753: Polygonella articulata was described (as Polygonum articulatum) by Linneus (Species plantarum 363);
1800: Polygonella polygama was the next species to be described (as Polygonum polygamum) by Ventenat (Hort. Cels 65);
1803: Polygonella was erected as a new genus by Michaux (FI. Bor.-Am. 2: 240);
1818: Polygonella gracilis was described as Polygonum gracile by Nuttall; however, that name was illegitimate and the species should be cited as Polygonella gracilis Meisn., since Meisner was the first to use a legitimate epithet (in DC. Prodr. 14: 80. 1856) and this is therefore to be taken as new (Wilbur 1988);
1821: Polygonella fimbriata was described (as Polygonum fimbriatum) by Elliott (Sketch Bot. S. C. & Ga. 1: 583);
1845: Polygonella americana was described (as Gonopyrum americanum) by Fischer and Meyer (Mem. Acad. St.- Petersb., ser. 6, 4:144);
1845: Thysanella , now a subgenus including the two species Polygonella fimbriata and P. robusta, had its origin as a generic name with Asa Gray (Boston J. Nat. Hist. 5: 232); 11
1856: Polygonella brachystachya (now P. polygama var. brachystachya) and Polygonella ciliata were described by Meisner (DC. Prodr. 14: 80);
1860: Polygonella croomii (now P. polygama var. croomii) was described by Chapman (FI. S. U.S. 387);
1896: Polygonella macrophylla was described by Small (Bull. Torrey Club 23: 407);
1909: Polygonella robusta (as Thysanella robusta) was described by J. K. Small (Bull. Torrey Club 36: 159);
1924: Polygonella basiramia (as Delopyrum basiramia; Bull. Torrey Club 51: 380) and Polygonella myriophylla (as Dentoceras myriophylla ; Bull. Torrey Club 51: 389) were described by J. K. Small;
1937: Polygonella parksii was described by Cory (Rhodora 39: 417);
1963: Horton (1963) reduced Small’s genera Dentoceras and Delopyrum to synonomy under Polygonella and Gray’s genus Thysanella to subgeneric status, and regarded Polygonella polygama as one highly variable species, not recognizing any varieties or subspecies (thus eliminating the epithetsbrachystachya and croomii). Horton also considered Polygonella basiramia to be a variety of P. ciliata and P. robusta to be a variety of P. fimbriata;
1981: Wunderlin (1981) reconsidered the Polygonella polygama situation and was able to discern three discrete entities, thus reinstating croomii and brachystachya as varieties under P. polygama',
1984: Nesom and Bates (1984) re-evaluated the species Polygonella fimbriata and P. ciliata (sensu Horton 1963) and elevated P. fimbriata var. robusta and P. ciliata var. basiramia to the species level again as P. robusta and P. basiramia, respectively, and concurred with Wunderlin’s treatment of the P. polygama complex.
O rganization o f t h e C h a p t e r s
Chapter I is a phylogenetic analysis of the genus Polygonella and the related group, Polygonum subg. Duravia. The parsimony criterion was used to 12 construct a conservative hypothesis of phylogenetic relationships among the
Polygonella species that requires the fewest possible ad hoc assumptions about character state change. Chapter II is a study of allozyme variation within the species Polygonella macrophylla , a rare coastal scrub plant endemic to the Gulf of Mexico coast between Carrabelle, Florida, and Gulf Shores, Alabama. This species was of special interest because of its apparent high inbreeding despite a gynodioecious breeding system. Chapter III is a comparison of gene diversity in
Polygonella with that found in other seed plants. Gene diversity was estimated from allozyme data for all eleven species of Polygonella and compared to the extensive data base on seed plant gene diversity surveyed by Hamrick and colleages. Chapter IV is the formulation of a biogeographical hypothesis involving the Pleistocene glacial history of North America to explain the unexpectedly low gene diversities displayed by the two northern widespread species of Polygonella , P. americana and P. articulata. This hypothesis was tested using gene diversity as the dependent variable in a multiple regression analysis involving independent variables scored for breeding systems, life span, geographic distribution, and latitude. 13
L it e r a t u r e c it e d
A b r a h a m so n , W. G. 1984a. Post-fire recovery of Florida Lake Wales Ridge vegetation. American Journal of Botany 71: 9-21.
A b r a h a m so n , W. G. 1984b. Species responses to fire on the Florida Lake Wales Ridge. American Journal of Botany 71: 35-43.
A b r a h a m so n , W. G., J o h n so n , A. F., L a y n e , J. N., a n d P e r o n i , P. A. 1984. Vegetation of the Archbold Biological Station, Florida: an example of the southern Lake Wales Ridge. Florida Scientist 47: 209-250.
H o r t o n , J. H. 1963. A taxonomic revision of Polygonella (Polygonaceae). Brittonia 15: 177-203.
Huck, R. B., Judd, W. S., W hitten, W. M, Skean, J. D„ Jr., W underlin, R. P., and D e la n e y , K. R. 1989. A new Dicerandra (Labiatae) from the Lake Wales Ridge of Florida, with a cladistic analysis and discussion of endemism. Systematic Botany 14: 197-213.
J a m e s , C. W. 1961. Endemism in Florida. Brittonia 13: 225-244.
J o h n so n , A. F., a n d A b r a h a m s o n , W. G. 1982. Quercus inopina: a species to be recognized from south-central Florida. Bulletin of the Torrey Botanical Club 109: 392-395.
K u r z , H. 1942. Florida dunes and scrub, vegetation and geology. Florida Geological Survey, Geological Bulletin 23: 1-154.
L a e s s l e , A. M. 1942. The plant communities of the Welaka area. University of Florida Press, Biological Sciences Series 4: 1-143.
L a e s s l e , A. M. 1958. The origin and successional relationship of sandhill vegetation and sand-pine scrub. Ecological Monographs 28: 361-387.
M il l e r , R. 1950. Ecological comparisons of plant communities of the xeric, pine type on sand ridges in central Florida. M.Sc. Thesis, University of Florida, Gainesville.
M y e r s , R. L. 1985. Fire and the dynamic relationship between Florida sandhill and sand pine scrub vegetation. Bulletin of the Torrey Botanical Club 112: 241-252.
M y e r s , R . L. 1990. Scrub and high pine. Pp. 150-193 in: M y e r s , R . L, a n d E w e l , J. J. (eds.), Ecosystems of Florida, University of Central Florida Press, Orlando.
M yers , R. L., and White, D. L. 1987. Landscape history and changes in sandhill vegetation in north-central and south-central Florida. Bulletin o f the Torrey Botanical Club 114: 21-32. 14
N e s o m , G. L., a n d Ba t e s , V. M 1984. Reevaluations of infraspecific taxonomy in Polygonella (Polygonaceae). Brittonia 36: 37-44.
Wh it n e y , M. 1896. The soils of Florida. U.S. Department o f Agriculture Bulletin 13: 14-27.
Wil b u r , R. L. 1988. The authority of the binomial Polygonella gracilis. Castanea S3: 167.
Wu n d e r l in , R. P. 1981. Polygonella polygama (Polygonaceae) in Florida. Florida Scientist 44: 78-80.
Z o n a , S., a n d Judd, W. S. 1986. Sabal etonia (Palmae): systematics, distribution, ecology, and comparisons to other Florida scrub endemics. Sida 11: 417- 427. Figure 1. Geographic distribution of Polygonella fimbriata (•) in Georgia, U.S.A., and P. robusta (■) in Florida, U.S.A.
15 16
Figure 1 Figure 2. Geographic distribution of Polygonella articulata in Illinois, Indiana, Iowa, Michigan, Minnesota, and Wisconsin, U.S.A., and southern Ontario, Canada.
17 Figure 2 Figure 3. Geographic distribution of Polygonella articulata in the northeastern United States and Quebec, Canada.
19 Figure 3 Figure 4. Geographic distribution of Polygonella parksii in Texas, U.S.A.
21 j
Figure 4 K> K> Figure 5. Geographic distribution of Polygonella americana in the southeastern United States.
23 Figure 5 Figure 6. Geographic distribution of Polygonella myriophylla in Florida, U.S.A.
25 26
Figure 6 Figure 7. Geographic distribution of Polygonella macrophylla in Alabama and Florida, U.S.A.
27
Figure 8. Geographic distribution of Polygonella polygama var. polygam (•),a P. polygam var.a croomii (■), and P. polygam var.a brachystachya (A) in the southeastern United States.
29 O Figure 8 Figure 9. Geographic distribution of Polygonella gracilis in Alabama, Florida, Georgia, and South Carolina, U.S.A.
31 32
Figure 9 Figure 10. Geographic distribution of Polygonella ciliata (•) and P. basiramia (!) in Florida, U.S.A.
33 34 • • k
Figure 10 CHAPTER I
CLADISTIC ANALYSIS OF POLYGONELLA AND ITS RELATIONSHIP TO POLYGONUM SUBG. DURAVIA
I ntroduction
Because of its logical and explicit methodology, the concept of cladistics has gained a large following since its principles were first put forth by Hennig
(1966). Highly-refined and efficient algorithms now exist for the purpose of reconstructing the evolutionary history of a group of organisms. These algorithms have been incorporated into several widely-distributed computer programs, e.g., PAUP (Swofford 1990), PHYLIP (Felsenstein 1989), and
HENNIG86 (Farris 1988). At the center of these approaches is the principle of parsimony: simply stated, if character state change is rare, then hypotheses involving extra assumptions of character state change ( i.e., parallel changes and reversals of character state) are to be discarded in favor of simpler hypotheses involving the minimal number of assumptions; extra assumptions of character state change are ad hoc and therefore undesirable in an explanation of character evolution w ithin a group (Wiley 1981:20).
In this study, I have estimated phylogenetic relationships among the species of two related plant taxa, the genus Polygonella and the subgenus
Duravia of Polygonum, one of many examples of disjunction between southeastern and western North America. A sound treatment of the taxonomy
35 36 and nomenclature of the genus Polygonella is available (Horton 1963); however, while Horton speculated about the evolutionary history of the group, no explicitly-derived phylogenetic hypothesis was put forward in his revision.
Benefits resulting from such an analysis include: 1) basic, systematic information about relationships among species useful in constructing classifications; 2) insights into the evolution of specific characters such as perenniality, dicliny, etc.; and 3) information useful in future phylogenetic biogeographical studies when compared with studies of other groups with similar distribution patterns. I am aware of only one published study that evaluated alternative historical explanations for the distribution of endemic
Florida plant species in light of cladistic hypotheses of phylogenetic relatedness
(Huck et al. 1989), and that study did not address the question of the western affiliations of Florida endemics. I will concentrate mostly on Polygonella , as the study of that genus forms the theme of this dissertation; however, some preliminary conclusions will be discussed including both the identity of that subgroup of Duravia that may have given rise to Polygonella and the degree to which the estimate of phylogeny reconstructed here agrees with the current taxonomy of Duravia.
Though intuitively appealing, there are several assumptions that one must make before the cladistic analysis begins, and, depending on the group under study (the ingroup ), these preliminary decisions (e.g., monophyly of the ingroup, outgroup selection, and character selection and scoring), may be more or less problematic. Common problems confronting investigators using cladistic methodology are: 1) the possibility that the group under study is not monophyletic; 2) the existence of more than one plausible outgroup; and 3) the difficulty of finding enough qualitative characters that can be unarbitrarily 37 polarized. As will be discussed in the following sections, the genus Polygonella is relatively free of these problems.
Monophvlv of Polveonella
Polygonella is most easily distinguished from Duravia in having internodal branching, connation of branch to stem for some distance beyond the node at which the branch arose. This condition is unique within the Polygonaceae
(Horton 1963), thus providing strong evidence that the species of Polygonella share a unique common ancestor. Other, less striking features separating
Polygonella from its closest relatives are (G. L. Nesom, pers. comm.):
■ Leafless inflorescences - no bracteal leaves occur in the congested inflorescences, in contrast to the related Polygonum subg. Duravia where inflorescences are usually uncongested and leaves, although diminished in size, do subtend the flower clusters;
■ Fibrous bundle sheaths - sclerenchyma fibers surround vascular bundles in the leaves of all species of Polygonella except P. articulata but are absent in all but one species of Polygonum subg. Duravia;
■ Thickened floral ochreae with the basal portion in a continuous cylinder - the only exception is Polygonella parksii in which the floral ochreae appear to be fused with the stem on one side;
■ Strictly one-flowered nodes - some species of Duravia have one- to three-flowered nodes with the former predominating.
As internodal branching is unknown elsewhere in the family, and the other synapomorphies are virtually absent from the related Polygonum species,
Polygonella may be safely considered a monophyletic group. The eleven species of Polygonella, as currently recognized, are:
Polygonella Michx. subg. Thysanella (Gray) Horton: P. fimbriata (Ell.) Horton P. robusta (Small) Nesom & Bates 38
Polygonella Michx. subg. Polygonella: P. americana (Fisch. & Mey.) Small P. articulata (L.) Meissn. P. basiramia (Small) Nesom & Bates. P. ciliata Meissn. P. gracilis (Nutt.) Meissn. P. parksii Cory P. macrophylla Small P. myriophylla (Small) Horton P. polygama (Vent.) Engelm. & Gray
Outgroup selection
As evidenced by pollen morphology (Plate I; Hedberg 1946) and stem anatomy (Haraldson 1978), Polygonella is most closely related to Polygonum sect.
Duravia (sensu Haraldson 1978), a group of 22 species, 20 of which are distributed entirely in western North America (two species, Polygonum douglasii and P. tenue, range eastward to Ohio). Haraldson (1978) went so far as to say,
"Polygonum sect. Duravia is anatomically more similar to Polygonella than to sect. Polygonum . . ." although she chose not to combine the two groups taxonomically. The close similarity palynologically as well as anatomically suggests that Polygonum sect. Duravia is the only plausible outgroup for
Polygonella. Polygonum sect. Duravia has recently been elevated to subgeneric status and two taxa (one new) have been recognized at the sectional level within that subgenus (Hickman 1984). To avoid undue confusion, I will hereafter refer to this group as simply Duravia, bringing up subgeneric and sectional levels only when comparing results with the published treatments of
Hickman (1984) and Haraldson (1978). The twenty-two taxa treated here as separate species are as follows:
Polygonum L. subg. Duravia (S. Watson) Hickman: P. austiniae Greene P. bolanderi Brew, ex Gray P. bidwelliae Wats. P. californicum Meissn. 39
P. cascadense Baker P. confertiflorum Nutt, ex Piper P. douglasii Greene P. engelmannii Greene P. esotericum Wheeler P. heterosepalum Peck & Ownbey P. kelloggii Greene P. majus (Meissn.) Piper P. minimum Wats. P. montanum (Small) Greene P. nuttallii Small P. paronychia Cham. & Schlecht. P. parryi Greene P. polygaloides Meissn. P. sawatchense Small P. shastense Brew, ex Gray P. spergulariaeforme Meissn. P. tenue Michx.
Character selection
Nineteen qualitative characters were found for which Duravia is
invariant, but for which Polygonella displays at least two states. Since one state
is invariant in the outgroup, it is possible to assign (unambiguously) ancestral
status to that state, and derived status to the state only found in the ingroup.
Thus, there is no shortage of characters in this group, as there are more than
twice the number needed to support all nodes of a fully-bifurcating, rooted
tree.
M a t e r ia l s a n d M e t h o d s
Characters scored
A data set comprised of a total of 45 vegetative and floral qualitative
characters (Table 1) was compiled for all 11 species of Polygonella and 22
species of Duravia. An unpublished data set compiled by Dr. Guy L. Nesom
(University of Texas, Austin) was used as the starting point for this analysis. 40
Revisions (Horton 1960, 1963; Hickman 1984) and an anatomical study of the
Polygonaceae (Haraldson 1978) were used as sources of potential characters for inclusion in the data set. A total of 19 characters (class A characters) were found to vary within Polygonella but were invariant within Duravia and, conversely, 14 characters (class B characters) were invariant within Polygonella but varied within Duravia. A third group of 12 characters (class C characters) varied in both Polygonella and Duravia.
Analysis of Polveonella
Outgroup selection
Because of the possibility that Polygonella originated from somewhere within Duravia (and the low probability of the converse), Duravia could be used as an outgroup for evaluating phylogenetic relationships within Polygonella, but
Polygonella could not be used as an outgroup for an analysis of Duravia. Using
Duravia as an outgroup for studying Polygonella is justified whether Polygonella and Duravia are related as sister groups or not. Only if Duravia arose from within Polygonella would the use of Duravia as an outgroup be untenable, and this is an unreasonable hypothesis in light of the number of synapomorphies uniting Polygonella. Thus, a single, consensus taxon representing all the species of Duravia was used as an outgroup for evaluating phylogeny within
Polygonella.
Characters included and information content
The taxon representing all of Duravia had the state common to all duravioid species for each of the class A characters, and the state ? (missing data) for all class C characters used. None of the class B characters were used 41 as they did not vary within Polygonella. In addition, one of the class C characters (habit erect or prostrate) was not included in the analysis of
Polygonella because it is autapomorphic (i.e., the only prostrate Polygonella is P. myriophylla). The homoplasy excess ratio (HER; Archie 1989b) was used to assess the phylogenetic information content of the data matrix. This measure compares the length of the most parsimonious tree to the average length of most parsimonious trees produced from similar data sets in which all phylogenetic information has been removed through randomization of character state assignments (Archie 1989a).
Establishment of functional outgroup
Although it was desirable to search all possible topologies (an exhaustive search) for trees having minimal length, enabling examination of the distribution of tree lengths, this type of search strategy was not practical for
Polygonella as a whole. The time involved in searching every possible topology becomes exorbitant with more than about nine taxa because the number of unrooted, binary tree topologies increases double-factorially with the number of taxa included (Cavalli-Sforza & Edwards 1967). The next best option
(branch-and-bound methodology) was used to find all minimum length trees
(MLTs) and these were used in the construction of a strict consensus tree.
Branch-and-bound techniques (Hendy & Penny 1982) represent the fastest search strategy known that is guaranteed to find all MLTs. The only drawback of the increased speed, however, is that branch-and-bound methods are not able to produce a distribution of tree lengths since they do not examine any topologies that are known to be longer than a tree already on hand. From the consensus tree, however, it was possible to identify a subgroup of the eleven 42
Polygonella taxa as a candidate for a functional outgroup (sensu Watrous &
Wheeler 1981). The reliability of this assessment was tested by counting the number of times the group appeared in 100 bootstrap replicates (Felsenstein
1985).
Analysis o f functional ingroup
Once a functional outgroup (and, by default, a functional ingroup) were identified for Polygonella , it was possible to do an exhaustive search on the taxa in the functional ingroup because of the reduced number of taxa involved.
A distribution of tree lengths was thus obtained for the ingroup. The MLTs obtained from this search were used in the construction of a strict consensus tree, which was considered to be the most conservative possible estimate of the phylogeny of Polygonella.
Analysis of Polveonum sube. Duravia
Taxa and characters included
A different tack was taken in the analysis of Duravia, since the use of
Polygonella as an outgroup could not be justified (Figure 1). The sister group relationship would pertain if Polygonella and Duravia were each monophyletic and shared a unique common ancestor. Note that in the case of a sister group relationship, the derived character is always correctly identified using outgroup analysis, whether the outgroup is taken to be Duravia (Figure 11 A) or
Polygonella (Figure 11C). The common clade relationship would pertain if
Polygonella originated from within Duravia, making Duravia paraphyletic since not all of the descendants of the most recent common ancestor are included in that group. In this case, the character identified as being derived is correct 43 only when Duravia is used as the outgroup (Figure 11B); using Polygonella as the outgroup makes the ancestral state appear to be derived (Figure 11D). The situation in which a subgroup of Polygonella gave rise to Duravia was not considered likely in view of several clear synapomorphies uniting the
Polygonella taxa, all of which would have had to undergo reversals under that scenario.
Construction of an unrooted tree was more appropriate here since the position of the root could not be determined without enlarging the scope of the study and using a more distantly related taxon as an outgroup. As it is always desirable (although not always possible) to include all members of the monophyletic group under study in a cladistic analysis, and since it could not be determined with certainty that Duravia was monophyletic without the inclusion of Polygonella , all taxa from both groups were included in the second analysis. All 45 characters in the data set were used in this analysis. Two class
C characters (anticlinal walls of sepal epidermal cells undulate or straight, and ratio of inner:outer mature sepal lengths 1:1 or 2:1) were autapomorphic for
Duravia but were not excluded since they varied within Polygonella.
Use o f topological constraints
Since a reasonably well-resolved estimate of phylogeny was available for
Polygonella from the previous analysis, the topology of all trees evaluated during subsequent analyses of the Polygonella/Duravia data set (hereafter referred to as the combined data set) was constrained by the Polygonella consensus tree. Thus, the only variation allowed in the Polygonella part of the combined data set was in different resolutions of the polychotomies present in the consensus tree (Figure 12). 44
Search strategy
The combined data set was searched heuristically because the large number of taxa (33) prohibited the use of even the relatively fast branch-and-bound method. Heuristic searches are not guaranteed to find the most parsimonious tree(s), but represent the best alternative in the case of large data sets (Swofford 1990). Heuristic searches proceed by finding an initial estimate of phylogeny quickly and then rearranging that tree to find out whether or not it represents only a local optimum. If it is only a local optimum, then there exist trees that are shorter than rearrangements of the original tree may discover. If a new, shorter tree topology is discovered during the course of these rearrangements, then the process is begun again using the new tree as a starting point. Once rearrangements can no longer find a shorter tree, the process stops and the current tree is considered the best possible estimate of the phylogeny (even though it may still represent a local optimum)
(Swofford 1990).
Hardware and software used
The analyses described above were performed on an Apple Macintosh
Ilci computer by the program PAUP (ver. 3.0L; Swofford 1990), with the exception of HER, which was calculated on an Intel 80286-based IBM-XT using the programs RANDOMIZ and SUMPAUP (supplied by James W. Archie) in concert with PAUP ver. 2.4 (Swofford 1985). The NEXUS data set used is reproduced in Appendix B. The options used during heuristic searches were: closest addition sequence; only one tree held at each step during the stepwise addition process; tree bisection-reconnection branch swapping; and MULPARS to force the program to save equally parsimonious intermediate trees and perform 45
TBR on each in turn. The steepest descent option was never used as it is much more likely to find locally (as opposed to globally) optimal trees (D. R.
Maddison, pers. comm.). All characters were treated as unordered except the class A characters used in the analysis of Polygonella , which were polarized by using Duravia as the outgroup. Declaring a transformation series as unordered is the most conservative option unless there is good reason to assume that the evolution of the character is constrained to follow a certain path; designating a character transformation series as ordered can only increase the number of steps in a tree (Maddison & Maddison 1989).
R esu lts
Relationships within Polveonella
The homoplasy excess ratio (HER) for the Polygonella data set was 0.623, indicating a substantial amount of phylogenetic information. An HER value of zero (0) indicates that the data are essentially random, a value of unity (1) indicates that there is no homoplasy at all in the data. The branch-and-bound algorithm found four most parsimonious trees at 51 steps. In these trees,
Polygonella fimbriata and P. robusta form a clade (monophyletic group) separate from (and sister group to) the clade comprising the other nine species of
Polygonella. These two clades correspond to the two subgenera currently recognized within Polygonella'. Thysanella and Polygonella (Horton 1963). The two species in Polygonella subg. Thysanella were grouped together in 100 out of
100 most-parsimonious trees generated from bootstrap data sets. The establishment of monophyly for Polygonella subg. Thysanella and P. subg.
Polygonella made it feasible to perform an exhaustive search including only the 46 nine species in the larger subgenus. The distribution of tree lengths (Figure 13) resulting from the evaluation of the 135,135 possible unrooted, binary tree topologies connecting the nine taxa revealed that there were four having the minimum length of 34 steps, 5 having 35 steps, 12 having 36 steps, and 15 having 37 steps. There was a sharp jump from 15 to 50 trees moving from 37 to 38 steps. This discontinuity was used as a cutoff point: trees with 37 or fewer steps were investigated further by means of consensus trees; trees with 38 or more steps were considered too homoplasious to be considered further. A semistrict consensus tree (= combinable-component consensus sensu Bremer 1990) for these nine taxa was constructed (Figure 14A) using the four trees of minimum length and found to be identical to a strict consensus tree made from the same set of 36 trees. To the base of the consensus tree constructed using the four minimum-length trees was added the two taxa comprising Polygonella subg. Thysanella, and to the base of that tree was added the outgroup Duravia
(Figure 14B). This composite represents the most conservative hypothesis of relationships based on the most thorough search feasible. To exhaustively search all eleven taxa in Polygonella would involve evaluating more than 34 million tree topologies.
Relationships within Polveonum sube. Duravia
Using the most conservative hypothesis of relationships from the analysis of Polygonella (Figure 14B) as a topological constraint, an heuristic search was performed on all species from both Polygonella (11 species) and
Duravia (22 species), using the search options described in the Materials and
Methods. The resulting 340 unrooted trees of minimum length 93 steps were reduced to a single semistrict consensus tree (Figure 15), rooted arbitrarily 47 between Polygonella and Duravia. Interestingly, Polygonella had the same fully- resolved topology in all 340 minimum length trees; the uncertainty about the affiliations of some species present in the Polygonella-o nly analysis were eliminated when the scope was enlarged and relationships among Polygonella species were evaluated in the context of character evolution in Duravia.
D isc u ssio n
Evolution of Polveonella
Chromosome numbers and phylogeny
The branching pattern for Polygonella determined by the heuristic search agrees well with groups based on chromosome number (Figure 16); this is encouraging since chromosome number was not used as a character in the analysis. In general, monophyletic assemblages within Polygonella have different characteristic chromosome numbers. The four basic monophyletic assemblages and the chromosome numbers of the species therein are: 1)
Polygonella fimbriata (FIM, n = 16) and P. robusta (ROB, n = 16); 2) P. articulata
(ART, n = 16), P. parksii (PAR, n = 18), P. americana (AME, n = 18) and P. myriophylla (MYR, n = 18); 3) P. polygama (POL, n - 14) and P. macrophylla
(MAC, n = 14); and 4) P. gracilis (GRA, n = 11,12), P. basiramia (BAS, n = 11), and P. ciliata (CIL, n = 11).
All of the chromosome counts cited above are from Horton (1960, 1963) except for those of Polygonella americana and P. myriophylla, which are from G.
L. Nesom (pers. com.), and one (P. parksii) reported here for the first time. The count of n = 16 for Polygonella articulata is atypical for the group ART-PAR-
AME-MYR, and perhaps should be recounted to confirm that it is indeed not n 48
= 18. There have been only three chromosome numbers reported from species
in Duravia: Polygonum tenue, n = 10 (Lflve & Lflve 1956); P. paronychia, n = 14
(Pojar 1973); and P. douglasii, n = 20 (Lflve & Lflve 1956, 1982). Thus, it is
unclear whether or not the range of chromosome numbers present in Polygonella
(n = 11, 12, 14, 16, 18) represents aneuploid reduction from n = 20, increase
from n = 10, or both from an intermediate number such as n = 14 or n = 16.
Since only one species of the eleven has a chromosome number atypical for its
group, the evolution of chromosome number has clearly been correlated with
morphological evolution in Polygonella, and, given that the phylogeny presented in Figure 16 is accurate, the ancestral number was most likely n = 16, the number characteristic of the most plesiomorphic lineage within Polygonella, P. subg. Thysanella (FIM-ROB). The distribution of chromosome numbers suggests that changes in chromosome number might have been responsible for some of the original speciation events giving rise to the ancestors of the four monophyletic assemblages of species.
Evolution o f perenniality
The evolution of perenniality within Polygonella is not clear-cut. The perennial condition appears to have evolved at least twice and perhaps three
times from annual ancestors (Figure 17). First, in Thysanella, ROB is perennial
whereas FIM is annual. It is possible, however, that both species have the capacity to be perennial, but it is only realized in ROB since the entire range of ROB is far enough south that hard freezes are avoided in winter. Thus, it is unclear which is the ancestral state in this complex. Second, in the group ART-
PAR-AME-MYR, the two perennial species (AME and MYR) clearly appear to be derived from an annual ancestor, since the switch to perenniality appears to 49 have occurred after the annuals PAR and ART branched off. This interpretation is complicated, however, if the scope is expanded to include the sister taxon of ART-PAR-AME-MYR, MAC-POL, which is entirely perennial.
It is unclear whether perenniality arose twice independently, once in ART-
PAR-AME-MYR and once in MAC-POL, or arose once and underwent reversal in the two annual members of ART-PAR-AME-MYR. Putting aside the problem of how many times perenniality arose, at least it can be said that the ancestral Polygonella was most likely annual. This agrees with the conclusions of Horton (1963) based on wood anatomy. Finding no evidence of paedomorphosis based on the criteria developed by Carlquist (1962), he concluded that ". . . evolution within the genus has been from herbaceous forms to woody species as well as to more advanced herbaceous types." (Horton 1963).
Perenniality is rare in Duravia: only Polygonum paronychia, P. shastense, and P. bolanderi are perennial; all nineteen other Duravia species are annuals.
The three perennials are widely separated on the consensus cladogram of Figure
IS, indicating that perennials tend to evolve from annuals in Duravia as well as in Polygonella.
Evolution of breeding systems
Breeding systems in Polygonella are quite varied for such a small genus.
Thysanella (FIM-ROB) is characterized by gynomonoecy. ART-PAR-AME-MYR is characteristically hermaphroditic, with PAR being exceptional in its gynodioecy. MAC-POL is comprised of a gynodioecious species, MAC, and a fully dioecious species, POL. Of the three annuals in GRA-CIL-BAS, GRA is dioecious while CIL and BAS are both gynodioecious. Thus, the ability to produce unisexual flowers appears to have been a characteristic of the ancestor 50 of Polygonella, as all four clades have at least one member species that does so, and dicliny apparently characterized the ancestor of Polygonella subg.
Polygonella, with the hermaphrodites having originated from diclinous
(probably gynodioecious) ancestors (Figure 18). The possible evolution of hermaphrodity from dicliny is quite unusual and invites further study. It is of course possible that the original ancestors of Polygonella were hermaphroditic
(resembling ART-AME-MYR) and, during the course of the evolution of the genus, speciation events involved the formation of a diclinous or gynomonoecious species from this hermaphroditic ancestor. This scenario does require an extraordinary amount of homoplasy in this character; however, the breeding system has clearly evolved rapidly with respect to most other characters and under even the most parsimonious resolutions it shows considerable homoplasy.
Phylogeny and geographic range
There is an interesting relationship between the estimated phylogeny and the extent of geographic distribution of species (Figure 19). Each of the four major clades in Polygonella includes a widespread (or regionally distributed) species as well as at least one narrow endemic. In one case, it appears as if the clade was ancestrally narrowly restricted in geographic range (e.g., ART-PAR-
AME-MYR) and in another clade the most advanced species are narrowly endemic (GRA-CIL-BAS). Duravia also has both very widespread species (e.g.,
Polygonum douglasii, which ranges from New England west to British
Columbia) and quite geographically restricted species (e.g.. Polygonum cascadense and P. heterosepalum). The phylogeny (Figure 15) of Duravia is so 51 unresolved, however, that it serves little purpose to speculate at this point whether widespread species are closely related to restricted species.
Phvloaenv and classification
The Polygonella part of the consensus tree resulting from the heuristic search (Figure 15) corresponds well with the classification proposed by Horton
(1963), in which FIM and ROB were placed in a subgenus, Thysanella, separate from the other species, which were placed in subgenus Polygonella. I concur with Horton (1963) that FIM and ROB are primitive within Polygonella ; however, based on the cladistic analysis, it appears that P. articulata is actually advanced within the genus with respect to most morphological features (in contrast to Horton). While Horton had only the features within Polygonella with which to base his conclusions, the context of this investigation included the related polygonaceous taxa in Duravia. The use of outgroup comparison was invaluable in this regard.
Very little previous work has been done on the western Polygonum species in subg. Duravia. This group is perhaps most noteworthy in that one species, Polygonum cascadense was shown to be predominantly ant pollinated
(Hickman 1974) and remains to date one of the few examples of this unusual pollination mechanism. All of the taxonomic attention to Duravia has resulted from the practical need for a classification to use in floristic treatments, especially for California (e.g. Jepson 1925; Munz 1973). The most recent treatment of the group was by Hickman (1984), expressly for the upcoming
(1993) revision of the Jepson Manual. Hickman recognized Duravia as a subgenus of Polygonum, and erected a new section ( Monticola) to oppose section
Duravia within the subgenus. He restricted sect. Duravia to the five species 52
characterized by 3-nerved, aculeate, linear, more-or-less recurved leaves lacking
the conspicuous basal joint of articulation. These species also have three
separate, hardened styles, persistent at least at the base, and occupy mostly
summer-dry lowland and foothill habitats (Hickman 1984). While Hickman did
not list the names of the five species he intended to be included in this section,
it must be assumed that he referred to Polygonum calif ornicum, P. bolanderi, P.
bidwelliae, P. parryi, and P. heterosepalum. These form a putative monophyletic
group that is more distantly related to Polygonella in the consensus tree of
Figure 15 than any other such group within Duravia. Remember that the tree
in Figure 15 is rooted arbitrarily between Polygonella and Duravia; it is thus
impossible to know (without expanding the scope of the study further) whether
sect. Duravia (sensu Hickman) is advanced or primitive within the Polygonella -
Duravia complex (»>., Polygonum calif ornicum could be the most like the ancestor of the entire complex), or even whether it is monophyletic. One can say, with some confidence, that these five species are the most distantly related of all the
Duravia species to Polygonella. For the remainder of this discussion, the terms
putative clade or putative monophyletic group will be used to indicate
monophyletic groups (clades) given that the placement of the true root is
actually between Polygonella and Duravia (as shown in Figure 15). Also, sect.
Duravia and subg. Duravia (sensu Hickman) will be used instead of simply
Duravia to avoid confusion.
Hickman’s sect. Monticola includes all other taxa of Duravia, which
Hickman viewed as being of subspecific status under two quite variable species,
Polygonum douglasii and P. polygaloides (rather than seventeen separate species as recognized in this study). Members of this section occur in foothill and montane habitats, and have 1-nerved, not aculeate leaves, the lowest of which 53 are usually lanceolate to round, with neither hardened nor persistent styles fused at the base (Hickman 1984). The lineage typified by Polygonum polygaloides comprises three other species (subspecies sensu Hickman): P. confertiflorum, P. esotericum, and P. kelloggii. These four taxa form a putative monophyletic group which has a sister-group relationship with sect. Duravia.
The five taxa recognized at subspecific rank by Hickman under Polygonum douglasii are here treated as six separate species: P. douglasii, P. spergulariaeforme, P. nuttallii, P. majus, and P. austiniae. Hickman considered
Polygonum sawatchense to be a synonym of P. douglasii subsp. johnstonii.
Unfortunately, either because their ranges do not include California (P. engelmannii, P. tenue, P. cascadense, P. montanum ) or because their overall morphology differs significantly from that typical for Duravioid species (P. shastense, P. minimum, P. paronychia ), Hickman did not discuss seven species considered here to be in subg. Duravia on the basis of anatomical (Haraldson
1978) and palynological (Hedberg 1946) data. It is assumed for the sake of comparison that these seven taxa would be placed by Hickman in sect.
Monticola. Hickman’s classification is incongruent with the results of the cladistic analysis reported here only in that the Polygonum polygaloides group of sect. Monticola shares more features (sepal stomata rarely present, lateral sepal veins absent, and pedicels short) with sect. Duravia than it does with the
Polygonum douglasii lineage within sect. Monticola. The validity of this assertion rests of course on the placement of the true root, which is unknown.
Hickman’s classification would be most compatible with the consensus tree of
Figure 15 if the actual position of the root were between the five taxa in sect.
Duravia and the group comprised of sect. Monticola and Polygonella. In this case, however, sect. Monticola would be paraphyletic without the inclusion of 54 the eleven Polygonella species. It is difficult to say more without further study of subg. Duravia and comparison with an outgroup that is outside of both
Polygonella and Polygonum subg. Duravia.
S u m m a r y
Based on palynological and anatomical evidence, the closest relatives of the eleven species in the genus Polygonella are the twenty-two species of
Polygonum subg. Duravia, distributed mainly in the northwestern United States.
Of a total of 45 morphological features (both vegetative and floral), 19 were able to be polarized (ancestral state identified) using the outgroup method.
Using these 19 plus 12 other (unordered) characters variable both in Polygonella and Polygonum subg. Duravia, a branch-and-bound search coupled with bootstrap analysis (heuristic searches of resampled data sets) established that
Polygonella subg. Thysanella (comprised of P. fimbriata and P. robusta) could be considered a functional outgroup for the other species in the genus (in
Polygonella subg. Polygonella). A rchie’s HER was 0.623, indicating that there was a substantial amount of phylogenetic information in the Polygonella data set. A semistrict consensus tree from the 36 shortest trees resulting from an exhaustive search of Polygonella subg. Polygonella was unresolved except for the grouping of P. americana with P. myriophylla and the grouping of P. gracilis with its two presumed derivative species, P. basiramia and P. ciliata. Because of the possibility that Polygonella was derived from some subgroup of Polygonum subg. Duravia, it was not possible to use Polygonella as an outgroup. Thus, a data set comprised of all 22 species of Polygonum subg. Duravia and the 11 species of Polygonella was searched heuristically, a constraint being supplied that limited rearrangements within Polygonella to those compatible with the 55 conservative estimate of phylogeny already obtained for Polygonella. This analysis resulted in 340 most-parsimonious trees, which were summarized using a combinable-component (^semistrict) consensus tree. Changes in chromosome number, life span, and breeding systems were evaluated in light of the relationships among Polygonella species suggested by this consensus tree. Even
though chromosome number was not used as a character in the analysis, the distribution of this character was highly corroborative of the tree topology and
indicated that the ancestral number for Polygonella was probably n = 16. Both perenniality and dioecy have apparently evolved more than once within
Polygonella, the ancestor of the genus being probably a diclinous annual. Each
of the four major clades within Polygonella have at least one widespread or
regional and one narrowly endemic species. Relationships within Polygonella
are concordant with the classification into two subgenera by Horton (1963).
Relationships within Polygonum subg. Duravia generally agree with the classification of Hickman (1984), although resolution was so poor in this part of
the consensus tree that little more can be said at this time. Of all the species in
Polygonum subg. Duravia, the five species in Hickman’s (1984) sect. Duravia are the most distantly related to Polygonella regardless of the placement of the root. 56
L iterature C ited
A r c h ie , J. W. 1989a. A randomization test for phylogenetic information in systematic data. Systematic Zoology 38: 239-252.
A r c h ie , J. W. 1989b. Homoplasy excess ratios: new indices for measuring levels of homoplasy in phylogenetic systematics and a critique of the consistency index. Systematic Zoology 38: 239-269.
B r e m e r , K. 1990. Combinable component consensus. Cladistics 6: 369-372.
C a r l q u is t , S. 1962. A theory of paedomorphosis in dicotyledonous woods. Phytomorphology 12: 30-45.
C a v a l l i -S f o r z a , L. L., a n d E d w a r d s , A. W. F. 1967. Phylogenetic analysis: models and estimation procedures. Evolution 21: 550-570.
F a r r is , J. S. 1988. Hennig86. Version 1.5. Port Jefferson Station, New York.
F e l s e n s t e in , J. 1985. Confidence limits on phylogenies: an approach using the bootstrap. Evolution 39: 783-791.
F elsenstein , J. 1989. PHYLIP (Phylogeny Inference Package). Version 3.2 Manual.
H a r a l d s o n , K. 1978. Anatomy and taxonomy in Polygonaceae subfam. Polygonoideae Meisn. emend. Jaretzky. Symbolae Botanicae Upsalienses 22: 1-95.
H e d b e r g , O. 1946. Pollen morphology in the genus Polygonum L. s. lat. and its taxonomical significance. Svensk Botanisk Tidskrift 40: 371-404.
H e n d y , M D., a n d D. P en n y . 1982. Branch and bound algorithms to determine minimal evolutionary trees. Mathematical BioSciences 59: 277-290.
H e n n ig , W. 1966. Phylogenetic systematics. Univ. of Illinois Press, Urbana.
H ic k m a n , J. C. 1974. Pollination by ants: a low-energy system. Science 184: 1290-1292.
H ic k m a n , J. C. 1984. Nomenclatural changes in Persicaria, Polygonum and Rumex (Polygonaceae). Madrono 31: 249-252.
H o r t o n , J. H. 1960. A monograph of Delopyrum Small, Dentoceras Small, Polygonella Michx., and Thysanella Gray (Polygonaceae). Ph.D. Dissertation: University of North Carolina, Chapel Hill.
H o r t o n , J. H. 1963. A taxonomic revision of Polygonella (Polygonaceae). Britlonia 15: 177-203. 57
H u c k , R. B., J u d d , W. S., Wh it t e n , W. M, S k e a n , J. D., J r ., W u n d e r l in , R. P., a n d D e l a n e y , K. R. 1989. A new Dicerandra (Labiatae) from the Lake Wales Ridge of Florida, with a cladistic analysis and discussion of endemism. Systematic Botany 14: 197-213.
J e p s o n , W. L. 1925. A manual of the flowering plants of California. Associated Students Store, Berkeley, California.
L o v e , A., a n d L o v e , D . 1956. Chromosomes and taxonomy of eastern North American Polygonum. Canadian Journal of Botany 34: 501-522.
L o v e , A., a n d L o v e , D. 1982. IOPB chromosome number reports LXXIV. Taxon 31: 120-126.
M a d d is o n , W. P., a n d M a d d is o n , D. R. 1989. Interactive analysis of phylogeny and character evolution using the computer program MacClade. Folia Primatol 53: 190-202.
M u n z , P. A. 1973. A California flora. Univ. of California Press, Berkeley.
P o ja r , J. 1973. Levels of polyploidy in four vegetation types of southwestern British Columbia. Canadian Journal of Botany 51: 621-628.
S w o f f o r d , D. L. 1985. Phylogenetic analysis using parsimony, vers. 2.4. Computer program and documentation, Illinois Natural History Survey, Urbana.
S w o f f o r d , D. L. 1990. Phylogenetic analysis using parsimony, vers. 3.0. Computer program and documentation, Illinois Natural History Survey, Urbana.
Watrous , L. E., a n d Wheeler, Q . D . 1981. The out-group comparison method of character analysis. Systematic Zoology 30: 1-11.
Wil e y , E. O. 1981. Phylogenetics: the theory and practice of phylogenetic systematics. John Wiley & Sons, New York. 439 pp. 58 Table 1. Characters and character states used in the cladistic analyses of Polygonella and Polygonum subg. Duravia.
1. Leaf apex: 0) thickened to edge; 1) with thin, hyaline rim; 2. Leaf margins: 0) relatively thick and opaque; 1) with thin, hyaline or slightly yellowish rim; 3. Leaf persistence: 0) persistent; 1) early deciduous; 4. Flanged depression in rachis: 0) absent or depression very poorly developed; 1) strongly developed; 5. Ocreola position: 0) appressed; 1) flaring; 6. Ocreal awns: 0) present; 1) absent; 7. Ocreal awn composition if awns present: 0) single vascular bundle; 1) triplet of vascular bundles; 8. Bracteoles: 0) present; 1) absent; 9. Floral morphology: 0) hermaphroditic; 1) gynomonoecious; 2) gynodioecious; 3) dioecious; 10. Flower base extended into a prominent tube: 0) absent; 1) present; 11. Outer sepal base shape: 0) cuneate to truncate; 1) auriculate; 12. Outer sepal position: 0) erect-appressed to somewhat spreading; 1) reflexed; 13. Transitional sepal: 0) usually absent; 1) present; 14. Sepal shape: 0) obovate; 1) narrowly oblanceolate-oblong; 15. Sepal margins: 0) entire to slightly wavy-crisped; 1) deeply fimbriate; 16. Inner three filament bases: 0) basally dilated; 1) gradually widening on all eight; 17. Inner three filaments: 0) smooth-margined; 1) with pair of projections or knobs; 18. Achene neck prominently extended: 0) absent; 1) present; 19. Achene surface (upper 1/5): 0) smooth; 1) pebbled; 20. Duration: 0) annual; 1) perennial; 21. Habit: 0) erect; 1) prostrate; 22. Leaf shape: 0) linear to narrowly lanceolate; 1) terete; 2) obovate to spatulate (generally); 23. Conical epidermal cells: 0) present; 1) absent; 24. Floral position at anthesis: 0) erect/spreading/arching; 1) deflexed/strongly nodding; 25. Anticlinal walls of sepal epidermal cells: 0) strongly undulate; 1) straight or curved; 26. Lateral sepal veins: 0) present (at least one pair); 1) absent; 27. Thickened, green sepal midrib: 0) present (at least on some plants; 1) absent; 28. Ratio inner:outer mature sepals: 0) 1:1; 1) about 2:1; 29. Style length: 0) long (0.4-1.0 mm); 1) short (0.1-0.2 mm to sessile); 30. Pollen grain length (average): 0) long (27-32 um); 1) short (16-21 um); 31. Achene length: 0) short (1.6-2.6 mm); 1) long (2.8-3.7 mm); 32. Leaf articulation (below congested inflorescence): 0) strong; 1) weak to absent; 33. Bracteal leaves fused basally to floral ochreae: 0) absent; 1) present; 34. Cuticle on lower leaf surface striate: 0) present; 1) absent; 35. Leaf margins: 0) planar; 1) revolute or sharply folded down; Table 1 (continued)
36. Leaf apex: 0) smooth to mucronulate or apiculate; 1) spine-tipped prominently in some; 37. Veins or ribs in ocreal setae: 0) present; 1) absent; 38. Ocreae margins: 0) entire; 1) erose or with linear segments; 39. Margin of bracteal leaves: 0) green; 1) white; 40. Pedicel length: 0) long (1-3 mm); 1) short (0-0.9 mm); 41. Length ratio of mature outer:inner sepals: 0) 1:1; 1) 2:1; 42. Style branches: 0) basally distinct; 1) basally connate; 43. Base of style branches: 0) not thickened, hardened or persistent; 1) thickened, hardened and persistent; 44. Achene color: 0) yellowish-brown; 1) pitch black; 45. Achene surface completely: 0) smooth-shiny; 1) striate-pebbled; Figure 11. Illustration of possible relationships between Polygonella and Duravia.
60 1 Duravia 1 Polygonella
O 0 0 0 1* 1*
IlllMIl Polygonella
0 0 0 0 1* 1*
Duravia Polygonella
1* l* o o o o
Duravia Polygonella o* o* 1 1 1 1
Legend 0 - actual ancestral state 1 = actual derived state * - state identified as derived using specified outgroup Outgrow
Figure 11 Figure 12. Illustration of the use of constraints in phylogenetic analysis. A. Consensus tree used as a constraint. B. Resolutions permitted under constraint.
62 63
A- A 3 C V £
Figure 12 Figure 13. The distribution of tree lengths resulting from an exhaustive search of all possible topologies.
64 65
34 (4) 35 (5) 36 (12) 37 (15) 38 (50) 39 (49) 40 (114) 41 (131) 42 (192) 43 (374) 44 (393) 45 (526) 46 (626) 47 (918) 48 (1087) 49 (1177) 50 (1731) 51 (1917) 52 (2333) 53 (2663) 54 (3300) 55 (4387) 56 (4257) 57 (4701) 58 (5274) 59 (5041) 60 (6626) 61 (6370) 62 (6460) 63 (8822) 64 (9316) 65 (11540)' 66 E S a B B H i (12552) 67 (10388) 68 (8318) 69 I (5706) 70 (5116) 71 (2350)
Figure 13 Figure 14. Consensus trees for Polygonella subg. Polygonella. A. Semistrict consensus of the four most-parsimonious trees. B. Semistrict consensus tree (rooted) of the 36 trees of length 37 or less.
66 67
P. artlculata A. P. parksii P. am ericana P. myriophylla P. macrophylla P. polygama P. gracilis P. ciliata P. basiramia
Duravia B. P. fimbriata P. robusta P. articulata P. parksii P. americana P. myriophylla P. macrophylla P. polygama P. gracilis P. ciliata P. basiramia
Figure 14 Figure 15. Semistrict consensus tree based on 340 equally most-parsimonious trees from an heuristic search of all taxa.
68 69
P.flmbriala subgenus Thysanella P. robust* ] P. articulate P. americana P. myriophylla P. paricsH subgenus P. poly gun* Polygonella P. macrophylla P. gracilis P. ciliata P. basiramia _/ Pm. califomicum Pm. bolsnderi section Pm. bidvelliae Duravia Pm. parryi Pm. heterosepalum Pm. polygaloides Pm. confertiflorum Pm. esotericum Pm. kelloggli Pm.tenue Pm. shastenso Pm. minimum Pm. douglasn section Montlcola Pm. spergulariaeforme Pm. nuttallQ Pm. mafus Pm. savatcbense Pm. austiniaa Pm. engelmannii Pm. paronychia Pm. montanum Pm.cascadense
Figure 15 Figure 16. Cladogram for Polygonella showing distribution of chromosome numbers.
70 71
fimbriata robusta N- 16 articulata americana myriophylla. N= 18 parksii polygama N- 14 macrophylla gracilis ^
ciliata N = 11 basiramia
Figure 16 Figure 17. Cladogram for Polygonella showing (bold lines) lineages leading to perennial species.
72 fimbriata robusta articulata americana myriophylla parksii polygama macrophylla gracilis ciliata basiramia
Figure 17 Figure 18. Cladogram for Polygonella showing distribution of breeding systems; species not labeled are gynodioecious.
74 75
fimbriata Gynomonoeclous robusta J articulata
americana Hermaphroditic myriophylla ^
parksii polygama ^ Dioecious macrophylla gracilis J Dioecious ciliata
basiramia
Figure 18 Figure 19. Cladogram for Polygonella showing the relative extent of geographic distribution for each species.
76 77
fimbriata
robusta articulata americana
m^ioph^la
paiksii polygama
macrophylla
gracilis
•ndemic ciliata
regional basiramia
widespread
Figure 19 Plate I. Comparison of scanning electron micrographs o f pollen from selected representatives of three major subgroups of Polygonum and Polygonella. Scale bar is 5 um. 1. Polygonum aviculare L. [Lewis 2141 (OS)]. 2. Polygonum pensylvanicum L. [Taylor-Lehman, no number (OS)]. 3. Polygonum paronychia Cham. & Schlecht. [Sundberg 2011 (TEX)]. 4. Polygonum californicum Meisn. [Arnaud, Jr., 19-Oct-1968 (TEX)]. 5. Polygonella robusta (Small) Nesom & Bates [Bozeman 11334 (SMU)]. 6. Polygonella fimbriata (Ell.) Horton [Hardin & Duncan 14328 (GA)]
78 79
Plate I CHAPTER II
ALLOZYME VARIATION IN THE RARE GULF COAST ENDEMIC POLYGONELLA MACROPHYLLA SMALL (POLYGONACEAE)
I ntroduction
Polygonella macrophylla Small is a perennial, diclinous, dicotyledonous flowering plant species described by J. K. Small from non-flowering material collected by A. W. Chapman along the coast of Florida, U. S. A. (Small 1896). It is the largest (in nearly all features) of the eleven species of the genus and has especially large leaves (hence the specific epithet). Polygonella macrophylla is rare, inhabiting the Gulf of Mexico from Carrabelle, Florida, west to Gulf
Shores, Alabama. The plants grow only in discrete stretches of a strip of coastal sand pine scrub habitat about 100-200 m in width and beginning about
50 m from the shoreline. The individuals are widely separated, often growing up through a dense layer of shrubby oaks such as Quercus myrtifolia Willd. and
Q. geminata Small. The majority of plants in each population bear bisexual flowers, but entirely carpellate (female) individuals are frequent (as high as
48%), making the species primarily gynodioecious, and entirely staminate (male) individuals have been reported (Godfrey 1988). The color of the calyx of this species is either entirely brilliant crimson red or mostly white with or without pink margins (flowers are entirely pink in some individuals). Horton (1960;
1963) and Godfrey (1988) both mention the existence of the two color morphs; however, neither author discusses the distribution of the color morphs
80 geographically. The two color forms never occur in the same population; only the populations near Carrabelle, Florida, are entirely comprised of the red flowered form whereas all populations west of Panama City, Florida, consist entirely of the white/pink flowered form (Figure 20). Thus the white/pink color morph is not rare, but is the color form in most of the range and in most of the populations of the species. The specimen of Chapman, used by Small in
his description of the species, was probably red-flowered since Chapman used the unpublished epithet rubra on several herbarium labels (Horton 1960:91). I
will use the unofficial designation "rubra" to refer to the deep, crimson-red
flowered morph in the vicinity of Royal Bluff and "alba" to refer to the
white/pink flowered morph occurring from the vicinity of Panama City
westward to Gulf Shores, respectively. While its flowers are often suffused
with red, indicating the probable presence of red flower color alleles, "alba" is clearly distinct in all cases from individuals of rubra, which have completely deep-red flowers with no hint of white.
The aims of this study were to: 1) compare the levels of gene diversity within and among populations of Polygonella macrophylla to that expected for a species with similar ecological traits; 2) to assess differences in the apportionment of gene diversity between the two color morphs; 3) to estimate levels of gene flow among populations (utilizing methods suggested by Slatkin and Barton 1989); and 4) gather other information about the population biology of this species useful in assessing the potential threat from human activities. 82
MATERIALS AND METHODS
Plant material for electrophoretic analysis was collected from six wild populations (Table 2) on three field trips. On the first trip, 28-29 October 1988, leaves were collected from plants in the wild and returned on ice to the
Archbold Biological Field Station in Lake Placid, Florida, where approximately
1 g of leaf material was ground in a mortar and pestle with a small quantity (1 ml) of M icrobuffer [Tris-HCl, 0.20 M; Sodium tetraborate (=borax), 0.029 M;
Sodium metabisulfite, 0.017 M; Sodium ascorbate, 0.20 M; Sodium diethyldithiocarbamate, 0.016 M; PVP-40, 5% vol/vol; 2-mercaptoethanol, 0.5% vol/vol; pH 7.5] (Werth 1985). The extracts were frozen on dry ice and shipped by express mail to the Ohio State University (OSU), Columbus, Ohio, where they were stored at -30 C until they could be analyzed electrophoretically. The second trip involved making a seed collection from the population at Gulf
Shores, Alabama, on 17 November 1988. The seeds were later germinated in the greenhouses of the OSU Department of Plant Biology. Of several hundred seeds planted, only 11 survived to a stage suitable for enzyme extraction. These were also ground in a mortar and pestle using 1 ml Microbuffer. The leaf material collected on the third trip (30 September 1989) was returned on ice to
OSU and ground using the method described above. These extracts were not frozen before electrophoresis.
Horizontal starch gel electrophoresis of the leaf extracts was carried out using 12% potato starch and two different gel/electrode buffer systems. The starch used was a 1:1 mixture of Electrostarch (Otto Hiller, Madison, Wisconsin,
U.S.A.) and StarchArt Corporation (Smithville, Texas, U.S.A.) starch. The electrode buffers used were: (1) Tris-EDTA-Borate [Tris, buffer grade, 0.65 M;
Boric Acid, anhydrous, 0.57 M; and EDTA, dihydrate , 0.016 M; pH 8.0] and (2) 83
Histidine Free Base-Citric Acid [Histidine Free Base, anhydrous, 0.065 M; and
Citric Acid, monohydrate, 0.0064 M; pH 6.5]. The gel buffers used were dilutions of the electrode buffers; 1:9 vol/vol electrode:distilled water for Tris-
EDTA-Borate and 1:3 vol/vol electrode:distilled water for Histidine Free Base-
Citric Acid. Tris-EDTA-Borate gels were run at a constant current of 50 mA overnight (10-14 hours); Histidine Free Base-Citric Acid gels were run at a constant voltage of 200 V overnight. Staining protocols from Soltis et al. (1983) allowed visualization of 6 different enzymes (10 putative genetic loci).
Enzymes observed best using the Tris-EDTA-Borate gel/electrode buffer systems were leucine aminopeptidase (LAP, EC 3.4.1.1, 1 locus), phosphoglucose isomerase (PGI, EC 5.3.1.9, 2 loci), triose phosphate isomerase (TPI, EC 5.3.1.1, 2 loci) and glutamate dehydrogenase (GDH, EC 1.4.1.2, 1 locus). Those observed best using the Histidine Free Base-Citric Acid gel/electrode buffer system were malate dehydrogenase (MDH, EC 1.1.1.37, 3 loci) and glyceraldehyde-3- phosphate dehydrogenase ([NADP]G3PDH, EC 1.2.1.13, 1 locus). Assessment of putative genotypes at each isozyme locus were made assuming the following subunit structures: monomeric (LAP), dimeric (PGI, TPI, MDH), hexameric
(GDH) and tetrameric (G3PDH) (Crawford 1990:78). Isozyme loci were numbered consecutively beginning with the most anodal locus when more than one isozyme was present for an enzyme. Allozymes (allelomorphs segregating within one isozyme locus) were also numbered sequentially starting with the most anodal form observed. After allele frequencies were estimated (Table 3), the following sample estimates were calculated: proportion of polymorphic loci
(P), weighted mean number of alleles per polymorphic locus ( Ap), weighted mean number of alleles per locus (A), mean gene diversity (//e) ( = mean expected proportion of heterozygotes in a population in Hardy-Weinberg 84 equilibrium), unbiased for sample size according to Nei (1987:179, eq. 8.6), weighted mean observed heterozygosity (Ho), and the number of unique alleles detected (Table 4). A gene diversity analysis was performed using equations 9
(p. 2SS) and 11 (p. 256) from Nei and Chesser (1983) to obtain sample estimates,
Hs and HT, of within-population and total diversity, respectively ( DST and CST were computed from Hs and 7/T) (Table 5), and sample estimates, D, of standard genetic distance (Nei 1972), were calculated according to equation 6 in Nei
(1978), which corrects for sample size (Table 6). The sample coefficient of inbreeding, / (Weir and Cockerham 1984), was used to measure departure from
Hardy-Weinberg expectation for each polymorphic locus in each population
(Table 7). The significance of departures of observed from expected heterozygosity was determined by the exact, one-tailed probability test of
Hardy-Weinberg equilibrium versus positive disequilibrium described by Weir
(1990:77-79). The Weir and Cockerham (1984; equations 1-4) method was used to obtain sample estimates, /, F and 0, of quantities comparable to Wright’s F- statistics Fls, Fjr and FgT, respectively. Estimates of gene flow ( Nm) were made using the private alleles (p(l)) or differentiation among populations (0 ,
CST) methods (Slatkin 1985; Slatkin and Barton 1989) (Table 8). The estimates,
Gst, of the coefficient of population differentiation were unbiased for sample size following Nei and Chesser (1983) and those of 6 were unbiased for sample size and population number following Weir and Cockerham (1984). All of the above were calculated using the program GENESTAT-PC (Lewis and Whitkus
1989, version 3.0) except Ho, f, 0 and Nm, which were calculated manually. 85
R e su l t s
In most measures of gene diversity, the two populations of "rubra" equal or exceed the four populations of "alba". In Table 4, estimates of the proportion of polymorphic loci (P), mean number of alleles per polymorphic locus (Ap) and per locus ( A), gene diversity (Ht), observed heterozygosity (Ho), and the number of unique alleles are listed for each population along with the mean for each color class. On average, "rubra" has about 91% more polymorphic loci, 9.8% more alleles per locus, more than twice as much gene diversity and 15 times more observed heterozygosity than does "alba". Estimates of within-population ( Hs) and within-species (//T) gene diversity were higher in
"rubra" than in "alba" (Table 5). The total gene diversity, //T, is equal to the sum of the within-population diversity ( Hs) and the among-population diversity
(Z)ST). The coefficient of gene differentiation among populations (CST) is calculated as Z>ST divided by HT and is thus that proportion of the total diversity that occurs among populations. While Hr and Hs were both greater in
"rubra" than in "alba", reflecting the pattern of greater genetic diversity revealed by P and A, relatively more diversity occurs among populations in
"alba" (Ds t = 0.0847; CgT = 0.547) than in "rubra" (Z>ST = 0.0620; GgT = 0.302).
The sample standard genetic distance ( D) was on average lower between populations of different colored flowers than between populations of the same flower color (Table 6). The standard genetic distance ranges from 0 to infinity and is the negative natural logarithm of the standard genetic identity (Nei
1987:220). Sample genetic distances ranged from 0.070 to 0.277 (means 0.156 for
"rubra" and 0.150 for "alba") for within-color-class and from 0.044 to 0.270
(mean 0.147) for among-color-class population comparisons. These mean values are closer to that expected for conspecific populations (0.051) than for 86 congeneric species (0.400) (Gottlieb 1981). There was a nonsignificant (p > 0.0S) negative correlation (r = -0.279) between the sample genetic distances and geographic distance.
The inbreeding coefficient (/) measures deviation from Hardy-Weinberg expected heterozygote proportions within a population, ranging from -1.0 (all heterozygotes) to +1.0 (all homozygotes), with an / value of 0 indicating identity with a population in Hardy-Weinberg equilibrium. One third of the estimates of / were significant at the 0.05 level (Table 7). All of the significant
/ values were positive, indicating deficiencies of heterozygotes (positive disequilibrium), and were about equally distributed between "rubra" and "alba".
These deficiencies were extreme in the case of "alba", where six of the seven / values were +1.0 (three were significant), indicating complete fixation. The mean / value for "alba" (0.897) was much higher than that for "rubra" (0.336).
Estimates (/ for FIg, F for FIT) of Wright’s F-statistics for the species revealed a high degree of inbreeding both within populations (/ = 0.439) and within the species (F = 0.805).
Of the methods in existence for estimating indirectly the level of gene flow taking place among natural populations, Wright’s FgT method and Slatkin’s private alleles method are the most accurate (Slatkin & Barton 1989). Wright
(1951) introduced the formula FgT = (1 / ( 4Nm + 1)) where Nm is the number of individuals moving among subpopulations every generation. Thus, Nm ■
[(l/FgT) - 1] / 4 provides a way to estimate gene flow indirectly through the use of Wright’s F-statistics. In Slatkin’s (1985) private alleles method, the average frequency of alleles present in only one population [p(l)] is used to estimate Nm through the use of a linear relationship between log10[p(l)] and log10[Am], determined by simulation experiments. For sample sizes close to 25, the 87 estimate of Nm is given by exp{[log10(p(l)) + 1.1] / -0.58} (Slatkin and Barton
1989). Slatkin and Barton (1989) suggest the use of CST or Weir and
Cockerham’s (1984) 0 in Wright’s formula, as both are good multilocus estimators of FST Three estimates of gene flow, two using Wright’s formula with both Gst and 0 and the third using Slatkin’s formula with p( 1), were calculated for "rubra" and "alba", both separately and combined into one large population with six separate subpopulations (Table 8). The estimate of the number of individuals migrating among populations each generation (Nm) varied from 0.229 to 0.578 in "rubra" and from 0.0673 to 0.207 in "alba".
Considered one large population ("rubraValba"), Nm varied from 0.121 to 0.230.
Wright’s method using GST always gave the highest estimates of Nm, while
Slatkin’s method using p(l) always gave the lowest. Estimates from none of these methods differed by more than 0.35 migrating individuals per generation, and, given the indirect nature of the methods, the values from all three were quite close; all predicted less than 0.6 migrant individuals between two populations per generation. Values of Nm, regardless of the method used, were always higher for "rubra" than for "alba" (on average, more than 2.7 times higher).
D isc u ssio n
Inbreeding and deviations from Hardv-Weinbere equilibrium
Of the 15 cases of polymorphism in which the inbreeding coefficient / was estimated, five represented significant (p < 0.05) deviations from Hardy- 88
Wienberg equilibrium and all of these were deficiencies of heterozygotes (or complete fixation in the case of the "alba" populations Grayton Beach, Destin, and Gulf Shores). Estimates of Fig and FIT for the entire species were both high, indicating extensive inbreeding within populations and the species, respectively. Inbreeding in this gynodioecious species can be due to either an increased rate of self-fertilization in hermaphroditic individuals or consanguineous mating (biparental inbreeding), possible in females as well as hermaphrodites.
In gynodioecious species, a high rate of selfing in hermaphroditic individuals could lead to increased selection for outcrossing (if inbreeding depression were significant), giving female individuals a selective advantage and thus allowing for higher frequencies of females in the population. Indeed, in Hawaiian Bidens , the proportion of female individuals in gynodioecious populations was significantly correlated with selfing rate in hermaphrodites
(Sun and Ganders 1986) and the average outcrossing rate was increased 9% by the presence of females (Sun and Ganders 1988). The frequencies of female plants in populations of these gynodioecious Bidens species (9-44%) were nevertheless higher than would be expected if the only factors were inbreeding depression and outcrossing rate. The frequency of females in two populations of Polygonella macrophylla (32% for Royal Bluff and 48% for G ulf Shores) were both higher than the mean of 28% calculated for Hawaiian Bidens (Sun and
Ganders 1986), suggesting a high selfing rate in the hermaphrodites of P. macrophylla.
Consanguineous mating is also a potentially important contributer to inbreeding, especially in populations recently founded by a single or very few individuals. At least two of the four "alba" populations appear to have been 89 recently founded (see below). The lack of any obvious seed dispersal mechanism (other than gravity) would be expected to promote mating among close relatives for some time after the period of initial colonization.
Differentiation among populations and gene flow
The high GgT values of 0.302 ("rubra") and 0.547 ("alba") indicate considerable population differentiation, with about 1/3 to 1/2 of the genetic variation of the species being among-population variation. Greater population differentiation often accompanies self-fertilized breeding systems; examples include Gilia (Schoen 1982) and Phlox (Levin 1978). Classifying Polygonella macrophylla as a sexually-reproducing, gravity-dispersed, long-lived, polycarpic perennial endemic to an early-successional habitat, one would expect GgT to be about 0.283 (Loveless & Hamrick 1984, Table 2, mean weighted by sample size), below even the lower value determined for "rubra". The highest mean GgT levels in the Loveless & Hamrick (1984) study resulted from predominantly selfing mating systems (GgT = 0.523), gravity dispersal (CgT = 0.446) and early successional stage (GgT = 0.411). Inbreeding is a factor common to all three of these, as selfers are completely inbreeding, gravity dispersal promotes biparental inbreeding in the absence of effective pollen dispersal, and selfing annuals are highly characteristic of early-successional habitats (Loveless &
Hamrick 1984). Thus, inbreeding has probably played a significant role in determining the apportionment of variation in this species.
Rates of gene flow in Polygonella macrophylla as a whole were estimated to be at most 0.578 ("rubra") and 0.207 ("alba") individuals migrating per generation between two populations, regardless of the method used. The rate of 90 gene flow is low enough in "alba" (4 Nm = 0.828 < 1) that genetic drift may have played a major role in determining the distribution of genetic variation among populations (Hamrick 1987). Geographically adjacent populations fixed for different alleles are found in both "rubra" (MDH-2) and "alba" (LAP) and cases of a population polymorphic for a locus adjacent to a population fixed for one of the alleles are also common (60% of polymorphic loci in "rubra" and 83% in
"alba”). Genetic drift due to founder effect or population bottlenecks may account for these fixation events, as well as the unexpected negative correlation between geographic and genetic distances (Table 6). Gene flow is estimated to be at least twice as great in "rubra" compared to "alba", which corresponds to the short distance between the two "rubra" populations, which is much smaller than the mean distance between pairs of "alba" populations.
Gene diversity and ecological traits
In a survey of 113 taxa, Hamrick et al. (1981) assessed the effects of various ecological traits on genetic variability measures. In their system,
Polygonella macrophylla would be classified as a sexually reproducing, noncultivated, long-lived perennial dicot endemic to an early-successional, xeric habitat, having a mixed mating system, animal pollination, medium fecundity
(102 to 10s), and a chromosome number between 10 and 20. On average, such a species would have about 33% polymorphic loci (P), 1.6 alleles per locus ( A) and a gene diversity (//e; referred to as PI, polymorphic index, by Hamrick et al.
1981) of 0.130. These values are averages of the means of each statistic over the 11 categories of Hamrick et al. (1981), weighted by the number of species and average number of loci used. The values obtained in this study for "rubra" 91 are very close to these figures ( P = 35.9%, A = 1.35, He ■> 0.131), but the values for "alba" are low enough to bring the mean values of P, A, and for the species down to 26.8%, 1.28 and 0.093, respectively. Due to the variance in the mean values of P, A and among the ecological characters treated by Hamrick et al. (1981), these numbers are not exceptional and can be explained by considering some ecological factors to be more important than others.
Unusually low P, A, and values result from endemism (P = 23.52; A = 1.43;
He - 0.086), xeric habitats (P = 15.39; A = 1.11; He = 0.048) and prim arily self fertilizing mating systems (P = 17.92; A = 1.27; He = 0.058) (Hamrick et al. 1981).
Thus, these factors may play a more important role in the amounts of genetic diversity displayed by Polygonella macrophylla than do other ecological traits, especially in "alba".
Lowered genetic variability in "alba" as compared to "rubra" might be attributable to selection, genetic drift in small populations, founder effects resulting from recent colonizations by small numbers of founding individuals, or lower sample sizes. The high differentiation among populations and low population sizes in Polygonella macrophylla are more suggestive of the effects of genetic drift than of selection. It is unlikely, however, that the lower gene diversity in "alba" compared with "rubra" is due solely to genetic drift since the population sizes in "alba" are comparable to those found in "rubra". The two westernmost populations of "alba", Gulf Shores and Destin, show the lowest diversity of all six populations. Founder effect provides a reasonable explanation for this lowered diversity since these two populations have no unique alleles and thus could have been founded recently. On the other hand, the sample sizes of these two populations were the smallest, and the smaller sample sizes could artificially reduce the estimated diversity because of the 92 greater chance of missing alleles in low frequency. Of the remaining two populations of "alba”, only Panama City shows a gene diversity similar to the two westernmost populations, although it differs in having a single unique allele present in low (3%) frequency. The sample size in the Panama City population was significantly higher than the two westernmost ones, yet the gene diversity was much lower than that in the remaining "alba" population, Grayton
Beach, in which gene diversity is comparable to the two "rubra" populations.
Grayton Beach has two unique alleles, suggesting that it has been separated from the other "alba" populations and from "rubra" for some time. It seems likely, therefore, that founder effect during recent colonization events, is the primary reason why three of the four "alba" populations have lowered gene diversity estimates. Gottlieb (1981) noted that self-pollinating species have much less genetic variability than outcrossers, although the reasons for this are not well understood since inbreeding per se does not change gene frequencies
(Li 1976:209). Thus, lowered diversity could also be due in some way to the higher levels of inbreeding detected in "alba" populations.
Future of the species
Polygonella macrophylla is restricted to very few localities and the population sizes are generally on the order of 50-100 individuals. The two
"rubra" populations, especially, are in danger of extinction. Development of the coastal dunes poses an immediate threat to the species (Godfrey 1978).
Polygonella macrophylla is currently listed as a category 1 species (U. S.
Department of the Interior 1985) and, as such, does not currently have endangered or threatened species status. Polygonella macrophylla is ecologically 93 important as one of the first species to become established and reach reproductive age after a fire and also is a potentially important ornamental plant adapted to xeric environments. The first steps toward bringing it into cultivation have been taken in an experimental program at Bok Tower Gardens,
Lake Wales, Florida (S. Wallace, pers. comm.).
S u m m a r y
Polygonella macrophylla is a rare, perennial, gynodioecious angiosperm endemic to a narrow zone of coastal scrub habitat along the Gulf of Mexico in
Florida and Alabama, U.S.A. The species is comprised of a red form ("rubra"), known from only two adjacent populations at the eastern distributional limit of the species, and a white flowered form ("alba") represented by several populations in the remainder of the species’ range. An electrophoretic investigation revealed that gene diversity in "rubra" is close to that expected given the combination of life history traits displayed by the species = 0.131) but is low if the white flowered populations are considered alone ( Ht = 0.059).
The lower genetic variability in "alba" may be attributed to higher amounts of inbreeding or a recent range expansion from a small number of individuals.
The high value of C?ST for the species (UST = 0.521) and especially for "alba"
(<7st = 0.547) indicates that most of the diversity is among populations. Lack of gene flow among populations, estimated to be less than 0.3 migrating individuals per generation, is a likely cause of greater population differentiation. The high Gsr values have implications for conservation in that several populations must be protected in order to preserve the genetic resources of this species. 94
L iterature C ited
C r a w f o r d , D. J. 1990. Plant molecular systematics: macromolecular approaches. John Wiley & Sons, New York.
G o d f r e y , R. K. 1978. Large-leaved jointweed. Polygonella macrophylla Small. Pp. 52-53 in: Wa r d , D. B. (ed.), Rare and endangered biota of Florida, Volume 5: Plants. Florida Committee on Rare and Endangered Plants and Animals, University Presses of Florida, Gainesville.
G o d f r e y , R. K. 1988. Trees, shrubs, and woody vines o f northern Florida and adjacent Georgia and Alabama. The University of Georgia Press, Athens, Georgia.
G o t t l ie b , L. D. 1981. Electrophoretic evidence and plant populations. Pp. 1-46 in: R e in h o l d , L., H a r b o r n e , J. B. a n d S w a in , T. (eds.), Progress in phytochemistry. Vol. 7. Pergamon Press, New York.
H a m r ic k , J. L. 1987. Gene flow and distribution of genetic variation in plant populations. Pp. 53-67 in: U r b a n sk a , K. M. (ed.), Differentiation patterns in higher plants. Academic Press, New York.
H a m r ic k , J. L ., M it t o n , J. B., a n d L in h a r t , Y . B. 1981. Levels of genetic variation in trees: Influence of life history characteristics. Pp. 35-41 in: Conkle, M. T, (ed.), Proceedings o f the symposium on isozymes o f North American forest trees and forest insects. Pacific Southwest Forest and Range Experiment Station, Berkeley, California.
H o r t o n , J. H. 1960. A monograph of Delopyrum Small, Dentoceras Small, Polygonella Michx., and Thysanella Gray (Polygonaceae). Dissertation, University of North Carolina, Chapel Hill.
H o r t o n , J. H. 1963. A taxonomic revision of Polygonella (Polygonaceae). Brittonia 15: 177-203.
L e v in , D. A. 1978. Genetic variation in annual Phlox: self-compatible versus self-incompatible species. Evolution 32: 245-263.
L e w is , P. O., and Wh it k u s , R. 1989. GENESTAT for microcomputers. ASPT Newsletter 2: 15-16.
Li, C. C. 1976. First course in population genetics. Boxwood Press, Pacific Grove, California.
L o v e l e s s , M. D., and H amrick , J. L. 1984. Ecological determinants of genetic structure in plant populations. Annual Review of Ecology and Systematics 15: 65-95. 95
N e i, M 1972. Genetic distance between populations. American Naturalist 106: 283-292.
N ei, M. 1978. Estimation of average heterozygosity and genetic distance from a small number of individuals. Genetics 89: 583-590.
N e i, M 1987. Molecular evolutionary genetics. Columbia University Press, New York.
N e i, M., and C h e s s e r, R. K. 1983. Estimation of fixation indices and gene diversities. Annals o f Human Genetics 47: 253-259.
S c h o en , D. J. 1982. Genetic variation and the breeding system of Gilia achilleifolia. Evolution 36: 361-370.
S l a t k in , M. 1985. Rare alleles as indicators of gene flow. Evolution 39: 53-65.
S l a t k in , M ., a n d B a r t o n , N . H . 1989. A comparison of three indirect methods for estimating average levels of gene flow. Evolution 43: 1349-1368.
Sm a ll , J. K. 1896. Studies in the botany of the southeastern United States - VII. Bulletin of the Torrey Botanical Club 23: 407.
S o ltis , D. E., H a u f l e r , C, H., D a r r o w , D. C., and G a s t o n y , G. J. 1983. Starch gel electrophoresis of ferns: A compilation of grinding buffers, gel and electrode buffers, and staining schedules. American Fern Journal 73: 9-27.
Su n , M, and G a n d e r s , F. R. 1986. Female frequencies in gynodioecious populations correlated with selfing rates in hermaphrodites. American Journal of Botany 73: 1645-1648.
S u n , M, and G a n d e r s , F. R. 1988. Mixed mating systems in Hawaiian Bidens (Asteraceae). Evolution 42: 516-527.
U n it e d St a t e s D e p a r t m e n t o f t h e I n t e r io r . 1985. Endangered and threatened wildlife and plants; review of plant taxa for listing as endangered or threatened species. Federal Register 50 (part 17): 46.
Weir, B. S. 1990. Genetic data analysis: methods for discrete population genetic data. Sinauer Associates, Inc., Sunderland, Massachusetts.
We ir , B. S., and C o c k e r h a m , C. C. 1984. Estimating F-statistics for the analysis of population structure. Evolution 38: 1358-1370.
Werth, C. R. 1985. Implementing an isozyme laboratory at a field station. Virginia Journal of Science 36: 53-76.
Wright , S. 1951. The genetical structure of populations. Annals of Eugenics 15: 323-354. 96
Table 2. Abbreviations used in the text, number of individuals sampled from each population (average sample size over all loci), and collection locality descriptions. Voucher specimen citations are italicized at the end of the locality descriptions.
Sample Abbreviation Size Description of locality
Red-flowered populations ("rubra"):
Royal Bluff 39.9 Florida, Franklin Co., Royal Bluff, 9.3 km west of Carrabelle City Beach, Lewis 2311.
Royal Dune 16.8 Florida, Franklin Co., sand dune ridge lying perpendicular to the coast, 8 km west of west end of bridge at Carrabelle, Lewis 2313.
White-flowered populations ("alba"):
Panama City 26.7 Florida, Bay Co., sand pine scrub on west side of Powell Road, off of U. S. 98 2.4 km east of State Route 79 at Panama City Beach, Lewis 2323.
Grayton Beach 17.0 Florida, Walton Co., along State Route 30A 1.4 km east of the junction of State Routes 30A and 283, Lewis 2432.
Destin 14.9 Florida, Okaloosa Co., north side of U. S. 98 5.5 km east of east end of bridge over the Choctawhatchee Bay at Destin, Lewis 2433.
Gulf Shores 10.2 Alabama, Baldwin Co., along State Route 182, 1.4 km east of junction of State Routes 182 and 161, east of Gulf Shores, Lewis 2398. 97
Table 3. Estimated allele frequencies for 10 loci among six populations of Polygonella macrophylla. Numbers of heterozygotes (G) and sample sizes (N) for each locus and population are indicated above the frequencies in the following format: G / N. Missing data are indicated by hyphens (—).
Royal Royal Panama Grayton Gulf Locus Allele Bluff Dune City Beach Destin Shores
LAP 4/40 1/12 0/39 0/27 0/24 0/11 a 0.300 0.458 0.000 1.000 1.000 1.000 b 0.700 0.542 1.000 0.000 0.000 0.000
G3PDH 0/40 0/20 0/12 0/28 0/26 0/11 a 0.000 0.025 0.000 0.000 0.000 0.000 b 1.000 0.975 1.000 1.000 1.000 1.000
PGM 0/40 0/17 0/38 0/6 0/22 0/12 a 1.000 1.000 1.000 0.830 0.450 1.000 b 0.000 0.000 0.000 0.170 0.550 0.000
PGI-2 24/39 6/15 4/32 0/9 0/24 0/12 a 0.385 0.233 0.064 0.110 0.000 0.000 b 0.615 0.767 0.906 0.890 1.000 1.000 c 0.000 0.000 0.030 0.000 0.000 0.000
TPI-1 0/40 5/17 0/40 0/6 0/12 0/6 a 1.000 0.559 1.000 1.000 1.000 1.000 b 0.000 0.441 0.000 0.000 0.000 0.000
TPI-2 0/40 0/19 0/40 0/0 0/0 0/6 a 1.000 1.000 1.000 —— 1.000
GDH 0/40 3/14 0/40 0/28 0/16 0/11 a 0.000 0.143 0.000 0.000 0.000 0.000 b 1.000 0.857 1.000 1.000 1.000 1.000
MDH-1 11/40 0/18 0/4 0/4 0/3 0/11 a 0.138 0.000 0.000 0.000 0.000 0.000 b 0.862 1.000 1.000 0.750 1.000 1.000 c 0.000 0.000 0.000 0.250 0.000 0.000
MDH-2 0/40 0/18 0/9 0/0 0/3 0/11 a 0.000 1.000 1.000 — 1.000 0.455 b 1.000 0.000 0.000 — 0.000 0.545
MDH-3 0/40 0/18 0/13 0/28 0/4 0/11 a 0.000 0.000 0.000 0.860 0.000 0.000 b 1.000 1.000 1.000 0.140 1.000 1.000 98
Table 4. Sample proportion of polymorphic loci (?), mean sample number of alleles per polymorphic locus (AJ, mean sample number of alleles per locus (A), sample gene diversity (tfe), unbiased for sample size following Nei (1987), sample observed heterozygosity (Ho) and number of unique alleles detected in populations and color classes in the species Polygonella macrophylla.
Unique Population P V A1 Ho alleles
Within "rubra” populations:
Royal Bluff 0.300 2.00 1.30 0.115 0.0977 1
Royal Dune 0.500 2.00 1.46 0.170 0.0893 3
Within "alba" populations:
Panama City 0.100 3.00 1.24 0.018 0.0150 1
Grayton Beach 0.500 2.00 1.35 0.149 0.000 2
Destin 0.111 2.00 1.16 0.055 0.000 0
G ulf Shores 0.100 2.00 1.11 0.052 0.000 0
Within color classes2:
"rubra" 0.359 2.00 1.35 0.131 0.0952 4
"alba" 0.187 2.42 1.23 0.0591 0.00627 43
^ e a n weighted by sample size. 2AU are weighted means except for number of unique alleles, which is a total, includes one allele (PGI'l, b) common to two "alba" populations 99
Table 5. Mean values for total sample gene diversity (//T), sample gene diversity within populations ( Hs), sample gene diversity among populations (2>ot)> and sample coefficient of differentiation among populations (Got) for all loci among populations in the "rubra" and "alba" color classes o f Polygonella macrophylla. All four estimates were calculated using equations 9 and 11 of Nei and Chesser (1983) to correct for sample size.
Color Class " s h t ^ST g st
"rubra" 0.143 0.205 0.0620 0.302
"alba" 0.0700 0.155 0.0847 0.547
Total ("rubra" + "alba") 0.0918 0.191 0.0997 0.521 100
Table 6. Above the diagonal: Geographical distances among the six populations of Polygonella macrophylla in kilometers taken as the shortest route following the Gulf Coast. Below the diagonal: Sample genetic distance ( D) values for pairwise comparisons of the six populations. Marginal values are mean distances from individual populations to the other five populations. The negative correlation (r = -0.279) between D and geographic distance is not significant (p > 0.05).
Royal Royal Panama Grayton Gulf Bluff Dune City Beach Destin Shores Means
Royal Bluff 2.8 130 158 186 288 153
Royal Dune 0.156 133 161 189 291 155
Panama City 0.136 0.044 29 56 158 101
Grayton Beach 0.216 0.216 0.277 28 130 101
Destin 0.270 0.107 0.162 0.135 102 112
Gulf Shores 0.096 0.094 0.143 0.110 0.070 194
Means 0.175 0.123 0.152 0.190 0.148 0.103 101
Table 7. Estimates of the inbreeding coefficient Fjc, which measures the correlation of genes within individuals within populations, using equation 1 of Weir and Cockerham (1984) for the polymorphic loci in Polygonella macrophylla. Significance levels of p < 0.05 are labeled with one (p < 0.05) or two (p < 0.001) asterisks (*); levels greater than p = 0.05 are not labeled.
Royal Royal Panama Grayton Gulf Locus Bluff Dune City Beach Destin Shores
LAP +0.767 ** +0.845 * -- -
G3PDH - + 1.000 -- - -
PGI-1 - - - + 1.000 +1.000 **
PGI-2 -0.288 -0.085 +0.281 +1.000 - -
TPI-1 - +0.429 --- -
GDH- +0.162 -- - -
MDH-1 -0.144 - - + 1.000 - -
MDH-2 - - - - - + 1.000 **
MDH-3 - - - + 1.000 ** - 102
Table 8. Estimated rates of gene flow (Nm) among populations of Polygonella macrophylla from two different methods, Wright’s FST and Slatkin’s private allele methods. For Wright’s (1951) FgT method, gene flow was estimated as Nm = [(l/FgT) - l]/4 by substituting GgT or 0 as estimators of F™ The GST used was unbiased for sample size following Nei and Chesser (1983) and 0 was unbiased for both sample size and population number following Weir and Cockerham (1984). Both were averaged across loci. For Slatkin’s private alleles method, gene flow was estimated as Nm - explO{[loglO(p(l)) + 1.1]/ -0.58) following the values recommended for a sample size of 25 by Slatkin and Barton (1989).
Method "rubra" "alba" Total ("rubra" + "alba")
Wright’s method using GST:
0.547 0.521 C ST 0.302 Nm 0.578 0.207 0.230
Wright’s method using 0:
0 0.489 0.681 0.652
Nm 0.261 0.117 0.133
Slatkin’s method:
P d) 0.187 0.380 0.270 Nm 0.229 0.0673 0.121 Figure 20. Map of western Florida and southern Alabama (U.S.A.) showing locations of populations of Polygonella macrophylla sampled for this study. Populations of "rubra" are labeled RB (Royal Bluff) and RD (Royal Dune). Populations of "alba" are labeled GS (Gulf Shores), D (Destin), GB (Grayton Beach), and PC (Panama City). That part of North America shown in detail is indicated on the inset map of North America.
103 Figure 20 CHAPTER III
ALLOZYME VARIATION IN THE GENUS POLYGONELLA: COMPARISON WITH OTHER SEED PLANTS
I ntroduction
Of the methods now available for detecting and quantifying differences among populations in gene diversity (e.g., recessive morphological markers, secondary chemistry, enzyme electrophoresis, restriction fragment length analysis, variable number tandem repeat analysis, DNA sequencing), enzyme electrophoresis remains the most cost-effective and least time-consuming if several to many populations are involved (Crawford 1990:324). DNA-based methods offer more precision than enzyme electrophoresis in that they uncover more of the genetic variation actually present. This is because close to 29% of mutations at the nucleotide level do not change the amino acid composition and thus are undetectable by electrophoresis (Nei 1987:29). However, it is possible to sample a species much more extensively with enzyme electrophoresis and thus obtain comparisons among species that would otherwise be too labor intensive or costly. Moreover, enzyme electrophoresis has distinct advantages over using secondary compounds and most morphological traits in that the genetic basis of the variation can be inferred in most cases (Crawford 1983). In a series of publications, J. L. Hamrick and his colleagues have presented the results of an extensive search of the plant electrophoretic literature, documenting both expected and realized levels of genetic diversity within and
105 106 among populations of a diverse array of seed plants (Hamrick et al. 1979;
H amrick et al. 1981; Loveless & Hamrick 1984; Hamrick & Godt 1989). The most recent of these endeavors (Hamrick & Godt 1989) documented levels of gene diversity at the species and population levels for seed plants classified according to eight reproductive, morphological, ecological, and taxonomic traits.
Before this kind of information was available, it was not known what was typical for a particular group of plants and it was thus difficult to make generalizations about possible causes for unusual levels of gene diversity.
Surveys such as these are important in enabling one to determine whether a given level of gene diversity is relatively high or low, but have the drawback that the data are drawn from a variety of laboratories, different subsets of gene loci, and plants that are usually not closely related (Karron 1987).
The primary objective of this study was to compare levels of gene diversity in Polygonella , both at the species and population levels, with values reported by Hamrick & Godt (1989) for the dual purpose of identifying atypical values and providing possible explanations for those anomalies.
Materials and M ethods
Populations sampled for this study
Table 9 gives population names, locations, and sample sizes for the
Polygonella populations sampled. Information about exact localities, dates visited, and associated species may be found in Appendix A.
The sample sizes given for the Polygonella articulata populations Omer,
Great Sand Bay, and Hampton, the P. americana populations Battiest, Malvern, and McDade, and the P. myriophylla populations Gun Club, Lake Ridge, and 107
Sun’N’Lake, represent all or very nearly all individuals present at the site.
Populations were selected so as to represent the range of each of the species as well as possible. The following sections outline the electrophoretic procedures and genetic diversity measures common to this chapter and the one that follows.
Starch gel electrophoresis
Extraction buffers used
For most of the duration of this project, a single extraction buffer recipe was used, namely that described by Werth (1985) called ’Microbuffer’ [Tris-HCl, 0.20
M; Sodium tetraborate (=borax), 0.029 M; Sodium metabisulfite, 0.017 M; Sodium ascorbate, 0.20 M; Sodium diethyldithiocarbamate, 0.016 M; PVP-40, 5% vol/vol;
2-mercaptoethanol, 0.5% vol/vol; pH 7.5], Leaf material from plants of
Polygonella articulata collected at the Indiana Dunes State Park site (Appendix
A) was extracted using the Gottlieb’s (1981) buffer as well as Microbuffer, and the two types of extracts were tested side by side on the same gel. Lanes corresponding to Gottlieb’s buffer showed no activity for any of the enzymes normally assayed (see below under heading "Enzymes assayed"), while those lanes corresponding to Microbuffer showed good activity for a number of enzymes. While there are quite a few differences between the two buffers, it is believed that the most important difference was the presence of dissolved PVP-
40 in Microbuffer and its lack in Gottlieb’s buffer. Even though the higher molecular weight PVP-360 was added directly to some of the extracts prepared using Gottlieb’s buffer, these extracts did not show improved activity for any of the enzymes assayed, suggesting that the phenolic compounds bound by dissolved PVP-40 in the MicroBuffer extracts act quickly enough that the 108
undissolved PVP-360 in Gottlieb’s buffer could not bind them before they destroyed most of the enzymes.
The reason that PVP-40 was singled out as the most important difference
was that a very simple buffer (hereafter referred to as TMP buffer) comprised
of only Tris [0.2 M], PVP-40 [5%] and 2-mercaptoethanol [1%] (pH 7.5) produced
results identical to that of MicroBuffer, whereas the same simple buffer
without the PVP resulted in loss of enzyme activity. Since the Tris and 2-
mercaptoethanol are ingredients in both Gottlieb’s buffer and MicroBuffer, it
was deduced that PVP was the one ingredient in MicroBuffer that made any
real difference with respect to Gottlieb’s buffer. Although it was never tried,
Gottlieb’s buffer with 5% dissolved PVP-40 would probably give results
identical to MicroBuffer.
Preparation and storage of extracts
Extracts were prepared using approximately 1 g of leaf material and a
small quantity (1 ml) of ice cold buffer. The leaf material was ground in a
mortar and pestle with the aid of a few grains of sterile sand. Extracts were
then stored in 1.5 ml microcentrifuge tubes in either an ultracold freezer (-30
C) or dairy case (4 C). No loss of activity was found in M icroBuffer extracts
after storage lengths of up to two months at 4 C over similar extracts frozen at
-30 C. Frozen extracts retained activity for much longer periods of time,
however.
Starch gel preparation and running conditions
Horizontal starch gel electrophoresis of the leaf extracts was carried out using 11% hydrolyzed potato starch and two different gel/electrode buffer systems. The starch used was usually a 1:1 mixture of ElectroStarch (Otto 109
Hiller, Madison, Wisconsin, U.S.A.) and StarchArt Corporation (Smithville,
Texas, U.S.A.) starch. Some gels were made using pure StarchArt starch, pure
Sigma starch (Sigma Chemical Co., St. Louis, Missouri, U.S.A.), or pure USB
(United States Biochemical Co., Cleveland, Ohio, U.S.A.) starch. The various types of starch differed in tensile strength (ElectroStarch is by far the strongest, StarchArt and USB the weakest) but all gave comparable results with respect to the enzyme mobilities observed.
Two electrode buffers consistently gave better resolution for more enzyme systems than other electrode buffers and were thus the ones most commonly used:
■ Tris-EDTA-Borate [pH 8.0, gel buffer 1:9 dilution] T ris, buffer grade, 0.65 M Boric Acid, anhydrous, 0.57 M EDTA, dihydrate , 0.016 M
■ Histidine Free Base-Citric Acid [pH 6.5, gel buffer 1:3 dilution] Histidine Free Base, anhydrous, 0.065 M C itric Acid, monohydrate, 0.0064 M
The gel buffers used were vol/vol dilutions of the electrode buffers with distilled water. Tris-EDTA-Borate gels were run at a constant current of 50 mA overnight (10-14 hours); Histidine Free Base-Citric Acid gels were run at a constant voltage of 200 V overnight.
Other buffer systems tried but not used more than a few times or for specific purposes were:
■ Morpholine [pH 6.1, gel buffer 1:19 dilution] Citric acid, monohydrate, 0.04 M N-3(3-aminopropyl)-morpholine, add until pH 6.1 (Useful in obtaining a better spread of MDH isozymes when necessary) 110
■ Lithium Borate [pH 8.2; gel buffer 1:9 dilution] Lithium hydroxide, monohydrate, 0.036 M Boric acid, 0.188 M (no better than Tris-EDTA-Borate and the everpresent borate band often obscured enzyme bands)
■ Histidine Citrate [pH 5.7; gel buffer 1:6 dilution] Histidine HCI, monohydrate, 0.048 M Citric acid, monohydrate, ca. 0.02 M, add until pH 5.7
■ Buffer systems 5 and 8 from Soltis et al. (1983) were not found to improve resolution over the Tris-EDTA-Borate and Histidine Free Base-Citric Acid buffers described above.
Enzymes assayed
Alcohol dehydrogenase (ADH, EC 1.1.1.1, dimeric) Aspartate aminotransferase (AAT, EC 2.6.1.1, dimeric) G lutam ate dehydrogenase (GDH, EC 1.4.1.2, hexameric) Leucine aminopeptidase (LAP, EC 3.4.1.1, monomeric) Phosphoglucomutase (PGM, EC 2.7.5.1, monomeric) Glucosephosphate isomerase (GPI, EC 5.3.1.9, dimeric) Triosephosphate isomerase (TPI, EC 5.3.1.1, dimeric)
GIyceraIdehyde-3-phosphate dehydrogenase[NADP] (G3PDH, EC 1.2.1.13, tetrameric) Isocitrate dehydrogenase[NADP] (IDH, EC 1.1.1.42, dimeric) 6-Phosphogluconate dehydrogenase (6PGD, EC 1.1.1.44, dimeric) Shikim ate dehydrogenase (SKDH, EC 1.1.1.25, monomeric) M alate dehydrogenase (MDH, EC 1.1.1.37, dimeric)
Isozyme loci were numbered consecutively beginning with the most anodal locus when more than one isozyme was present for an enzyme. Allozymes
(allelomorphs segregating within one isozyme locus) were also numbered sequentially starting with the most anodal form observed.
Staining protocols from Soltis et al. (1983) allowed visualization of the following enzymes (not all visualized for every population). Enzyme abbreviation, nomenclature (Florkin & Stotz 1965), and the subunit structure used for purposes of genetic interpretation ( i.e., that commonly observed in other plants; Crawford 1990:78) are given in parentheses after the name. Ill
Enzymes not listed here (but which were able to be scored for some species) are explained in the Materials and Methods of the appropriate chapter(s).
Gene diversity measures estimated
After allele frequencies were estimated, gene diversity was estimated following Hamrick & Godt (1989), who used standard (not unbiased for sample size) estimates of allelic and gene diversity such as P, A and H and measured these at the level of the population and the species. Since gene diversity
(expected proportion of heterozygotes in a theoretical Hardy-Weinberg population) is affected by both P and A, but also is responsive to the evenness of gene frequencies (Brown & Weir 1983), it was used as an overall measure of genetic variation in this study.
Species-level gene diversity, HT - This is theH T of Nei (1973) not corrected for sample size or number of populations and averaged over all loci. //T is the expected proportion of heterozygous individuals in a single population comprised of all individuals in a species, if that population were in Hardy-
Weinberg equilibrium. Throughout the following discussion, this quantity will be referred to simply as HT, but it must be remembered that it is referred to as
//eg in Hamrick & Godt (1989); HT as reported by Hamrick & Godt (1989) differs in that it is an average over the polymorphic loci only.
Population-level gene diversity, Hs - This is theHs of Nei (1973,) not corrected for sample size or number of populations and averaged over all loci. H s is the
Hardy-Weinberg expected heterozygosity averaged across all populations sampled. This quantity is equivalent to of Hamrick & Godt (1989) and, again, Hs reported in Hamrick & Godt (1989) is different in that it is an average over polymorphic loci only. 112
Coefficient of gene differentiation, CST - Since Hamrick & Godt’s (1989) values for gene diversity at the species level are equivalent to Nei’s Hr (not corrected for sample size), and their population-level gene diversity (H) is ®P equivalent to a biased Nei’s H„, the value (// - H) / // is thus equivalent to 9 CS « p «l CgT (not corrected for sample size). GgT is the same whether averaged over all loci or only polymorphic loci and measures the amount of genetic differentiation among populations of a species.
Traits scored
Of the eight traits scored by Hamrick & Godt (1989), three varied significantly among species in Polygonella : life span, breeding system, and extent of geographic distribution. Life span was categorized for each species as either annual or perennial. Breeding systems in Polygonella were classified as either hermaphroditic (all flowers bisexual), gvnomonoecious (all plants bearing some unisexual female flowers but most flowers on each plant bisexual), gvnodioecious (most plants in a population with only bisexual flowers, but some proportion of the individuals bearing only unisexual female flowers), and dioecious (all individuals bearing only unisexual flowers, either all male or all female). While these categories easily and unambiguously scored for Polygonella species, it was not possible to compare them directly with the categories used by
Hamrick & Godt (1989), which were defined on the basis of degree of self- fertilization. Dioecious species must be fully outcrossing, however, in each of the other breeding system categories above, there is not a direct correspondence between breeding system and degree of selfing (i.e., mating system). Extent of geographic distribution is a relative measure, widespread meaning different things to different workers. Since Hamrick & Godt (1989) did not calibrate 113 their categories, it was not possible to judge the degree to which the categories set up for Polygonella were comparable to those set up by Hamrick & Godt
(1989). ThePolygonella species classified as widespread were those covering an area approximately equivalent to one fourth the area of the 48 contiguous
United States. These species were not continuously distributed over this area.
Regional species in Polygonella are those covering an area approximately half that of the widespread species. Endemic species were those having a total distribution about the size of Rhode Island, or smaller. Several of the endemic species have very long, narrow distributions because of specificity to a particular habitat or soil type (e.g., Polygonella parksii occurs only on the narrow strip of Carizzo sand extending from Normangee southwest to
Pleasanton in Texas).
Hardware and software used
All computations were performed using an IBM-XT Personal Computer equipped with an Intel 8087 math coprocessor. All gene diversity statistics were calculated by the program GeneStat-PC (Lewis & Whitkus 1989), version
3.2. H and H were computed using the "Polymorphism indices" option, HT, Hs,
DgT, and Gs t using the "Gene Diversity Statistics: Unmodified" option, and Hm and H using the "Hamrick & Godt analysis" option.
R esults and Discussion
An average of 6.6 populations per species, 11.4 loci per population, and
14.3 individuals per locus per population were sampled electrophoretically in this study (Table 10). The most thoroughly sampled species was Polygonella articulata (10 populations, 13.2 loci/pop., 22.4 individuals/pop./locus). Although 114
an attempt was made to select populations of P. articulata so th at the entire
range was sampled, it was not possible to have material from both the western
and eastern extremes of the species’ distribution available for electrophoresis at
the same time. Data from the three western populations were combined with
the data for the seven eastern populations by assuming, for each locus, that the
most common allele from both regions was, in fact, identical. This provided an
accurate estimate only for //g; the estimates of HT and GST are minimum
estimates of the parametric values of these statistics. Any divergence between
the eastern and western populations is obscured by this procedure, and,
depending upon the degree of divergence, //T and CgT for this species might be
in actuality quite higher than reported here. The least thoroughly sampled
species was Polygonella ciliata (2 populations, 12.0 loci/pop., 4.2 indivi-
duals/pop./locus). It is likely that this low sample size caused diversity
estimates to be artificially lowered. Also, the sampling of only two populations
of both P. ciliata and P. basiramia maximizes the variance (minimizing the
reliability) of estimates of C7gr
With these caveats, I will first compare diversity in Polygonella with
what is typical for seed plants in general (and dicots in particular). The
sections following that deal with three traits that vary among Polygonella
species, each of which is expected to influence the amount and/or distribution
of gene diversity. For each, I will discuss first the expectations, second, the
observed values for both seed plants (from Hamrick & Godt 1989) and
Polygonella , and third, possible reasons for exceptional observations and deviations from expectation.
Figures 21-30 show both the relationship between gene diversity in
Polygonella and the species traits life span, breeding system and geographic 115 distribution, and the relationship between diversity in Polygonella and that typical for similar categories of seed plants. Each figure shows values for
Polygonella species as vertical white stripes along a solid-black, horizontal bar, the mean being indicated by an open, unlabeled vertical rectangle. Values for seed plants obtained from Hamrick & Godt (1989) are displayed somewhat differently. Since sample sizes for that study were quite large (over 100 species per category), the central-limit theorem justifies the assumption of approximate normality for the sample proportion parameter of a binomial random variable
(Mendenhall & Scheaffer 1973:270). Thus 95% confidence intervals were constructed for each mean and represented in the horizontal dimension of an open, rectangular box. Within each such box is given the mean and category of seed plant for which the mean was calculated. In Figures 22 - 30, overlapping boxes imply that the means within the boxes are not significantly different at the 0.05 level. In cases where confusion results from that convention, lower case letters are used to indicate which means are significantly different.
Gene diversity at the species level (//T) averaged 0.1304, diversity at the population level ( ) averaged 0.757, and the mean proportion of gene diversity among populations (CgT) was 42.0% (Table 10). Polygonella shows on average less diversity and more population differentiation (at both the species and population levels) than either all seed plants or just dicots (Figure 21), however the range of values is clearly large. Assuming equal variances and approximate normality, means of HT and Hs for Polygonella species are not significantly different from means for seed plants or dicots. The mean C?ST for Polygonella species is significantly higher than the mean for seed plants (P < 0.05); however, it is not significantly different than the mean for dicots. While HT values are more or less evenly distributed across a range from nearly zero to 116 over 0.200, values for HB are either quite low (Polygonella ciliata, P. articulata, P. americana ), quite high (P. myriophylla), or intermediate (all others). The three species with low values for both HT and Hs have very little in common:
Polygonella ciliata is an endemic, gynodioecious annual, P. articulata is a widespread, hermaphroditic annual, and P. americana is widespread and hermaphroditic, like P. articulata, however it is perennial. Polygonella ciliata may have an exceptionally low estimated diversity as a result of low sample size. A possible explanation for the low diversity in the two widespread species will be discussed below and (more extensively) in Chapter IV. GgT values cover nearly the entire spectrum, with P. fimbriata and P. myriophylla having the lowest values and P. ciliata and P. americana the highest.
Allozvme variation and life soan
Predictions
It was predicted that the perennials, Polygonella americana, P. myriophylla, P. polygama, P. macrophylla, and P. robusta would display higher levels of genetic diversity and lower population differentiation than the annuals, all other things being equal. This is because the genetic neighborhood size (Ne) in annual plants is less than that in perennials (Loveless & Hamrick
1984), since, in perennials, the variance in parent-offspring distances is larger because of multiple opportunities for mating with distant individuals. Long- lived populations will also be less susceptible to drift. Assuming that an annual and perennial do not differ in the number of gametes presented each generation, the total number of gametes produced during the lifetime of the perennial would be n times that of the annual, where n is the number of generations in which the perennial was able to produce gametes. This increased 117
"sampling error" means that annuals suffer a greater decay of genetic variance than do perennials, all other things being equal (Loveless & Hamrick 1984).
Greater genetic drift means a higher variance in the frequency of a particular allele among populations of a species, hence a higher (?gT, for annuals.
Observations
Predicted levels of diversity were realized in seed plant Hs values
(Figure 23), in which long-lived perennials had significantly higher diversity than did annuals or short-lived perennials. Seed plant annuals had, however, much higherHr values than short-lived perennials (Figure 22), and were not significantly different from the long-lived perennials for this measure. This is in accord with the prediction of higher genetic drift in annuals. Population differentiation, accompanying random fixation events produced by drift, increases HT without concomitantly increasing Hs. Annual seed plants have the highest Gst, followed by short-lived perennials and then long-lived perennials
(Figure 24).
Perennials, on average, were higher for both HT (Figure 22) and Hs
(Figure 23) in Polygonella. For Hr , Polygonella annuals had on average much less diversity than is typical for seed plants. The mean would have been greater had P. articulata and P. ciliata been omitted; as discussed above, both of these species haveHT estimates that are probably artifactually low.
Polygonella ciliata and P. articulata also cause the unusually lower H& for annual polygonellas; however, this time the value for P. articulata cannot be considered artifactual. For the perennials, P. americana is primarily responsible for the low Hs mean (and low HT mean) for perennial polygonellas. The mean
Hs for the perennials is nevertheless within the 95% confidence region for 118 short-lived herbaceous perennials. Polygonella myriophylla is the only
Polygonella w ith an Hs value typical of long-lived woody perennials.
The pattern seen in CST for seed plants (predicted pattern) was not reflected in Polygonella, in which perennials had a higher average <7gT than did the annuals, although not by a great margin. The mean <7ST for annual
Polygonella species was within the 95% confidence interval found for seed plants, whereas that for the perennial polygonellas was much higher than that typical for even an herbaceous, short-lived perennial. Thus, an explanation for the deviation from prediction probably lies in the three perennials with a relatively high GST (Polygonella polygama, P. macrophylla and P. americana), and not in the annuals.
Polygonella macrophylla appears to have a mating system characterized by much inbreeding, either uni- or biparental, or both (see Chapter II). An unusual amount of inbreeding would produce unusually high population differentiation (and thus higher (7gT) as the result of increased genetic drift.
The low population sizes in this species (only 16 individuals in the Royal Dune population) compound the effects of inbreeding.
The higher CgT of Polygonella polygama is likely due to a combination of low sample size and founder effect. The numbers of individuals able to be scored electrophoretically was low for several populations (average less than 10 for all populations except White Oak and Oak Park). Lower sample sizes lead to undetected alleles and artifactual variance among populations in the frequencies of alleles. In addition, the further inland a population of P. polygama, the less diversity detected. This relatively low diversity found in the inland populations compared to coastal or peninsular populations was not the result of low sample sizes, as close to 20 individuals were sampled from two of 119
the three populations with the lowest gene diversity values. These inland
populations were probably founded relatively recently, causing diversity to be a
function of the number of alleles carried by the founding individuals. If some
populations have a single allele fixed at many loci due to founder effect, then
Gst is increased solely though the effect of "sampling error" in the founding
individuals.
Genetic drift due to low population size was likely responsible for the
high (7st in the species Polygonella americana. Populations of this species are
quite isolated from one another and, in some cases {e.g., Malvern and Battiest),
population sizes are below SO individuals. In such small populations in which
the chance of receiving immigrant alleles is very low, biparental inbreeding
eventually leads to fixation of alleles at many loci (note the extremely low
value of population-level gene diversity, Hs, for this species in Figure 23).
Allozvme variation and breeding system
Predictions
The breeding system of an organism is certain to strongly influence both
the amount and apportionment of genetic variation (Wright 1940, 1943; Loveless
& Hamrick 1984). Excessive amounts of self-fertilization or biparental
inbreeding increases the correlation among uniting gametes, leading to subdivision of populations (and, on a larger scale, species) into small, isolated
neighborhoods. This decreased neighborhood size results in a loss of genetic
diversity as allele frequencies become more extreme and alleles are lost.
Homozygous genotypes predominate in highly selfing populations, increasing
the chance that individuals founding new populations are not carrying all of
the alleles present in the ancestral population, leading to populations that are 120 excessively low in genetic diversity. Thus, populations of highly selfing hermaphrodites would be expected to harbor less diversity at both the population level and the species level; however, the lack of diversity at the population level probably would be the most pronounced. Populations of mixed-mating hermaphrodites or gynodioecious/gynomonoecious species would have higher levels of diversity within both populations and species, and the highest values for HT and H s would be expected for dioecious species and self- incompatible hermaphroditic and gynodioecious species.
The variance in gene frequency among populations (i.e., population differentiation) reaches its maximum when there is complete selfing
(inbreeding coefficient F = 1) and, at the other extreme, is minimal (no differentiation among populations) when there is complete panmixis (F = 0)
(Wright 1943). Thus, a completely-selfing hermaphrodite should be at one extreme (high values of CgT), with dioecious and self-incompatible species at the other (low population differentiation); hermaphrodites with mixed mating systems (or self-compatible gynodioecious or gynomonoecious species) should fall in between these two extremes.
Observations
In accordance with prediction, obligate selfers had significantly lower total diversity (//^ Figure 25) than wind-pollinated, mixed-mating seed plants, and significantly lower intrapopulational diversity (//g; Figure 26) than either obligate outcrossers or wind-pollinated mixed-mating seed plants. The situation is not uncomplicated, however, since obligate-outcrossing seed plants have levels of both //T and Hs that are intermediate between obligate selfers and wind- pollinated, mixed-mating species. The explanation for this is found by 121 inspection of GST values (Figure 27) for seed plants. Selfers have a much higher mean <7ST than either mixed-mating or outcrossing species, as expected.
However, it is obvious that the mating system is not nearly as important as the pollination mechanism when it comes to mixed-mating and obligately outcrossing species. Wind pollinated seed plants have significantly lower GST values, and thus less population differentiation, than do animal pollinated species regardless of whether they are mixed-mating or obligately outcrossing.
This accounts for some of the complications in HT and Hs values, but does not adequately explain why wind-pollinated, obligate outcrossers have significantly less intrapopulational gene diversity than do wind-pollinated mixed-mating species.
In Polygonella, the observed mean HT values could not be much closer to what was predicted: the obligately outcrossing dioecious species harbor the greatest total diversity, the hermaphrodites (assumed to be self-compatible and mixed-mating), show the least total diversity, and the species with intermediate gynomonoecious or gynodioecious breeding systems (probably mixed-mating to predominantly outcrossing) have intermediate //T values.
Gene diversity for the dioecious polygonellas (which would be classified as outcrossing animal-pollinated seed plants) was high at the species level (//T;
Figure 25), due to the high population differentiation in P. gracilis and low at the population level (7/g; Figure 26), being more typical of mixed-mating rather than outcrossing species. This combination gives a {7gT for the dioecious polygonellas so high that it is high even for selfing seed plants (Figure 27).
Both of these species have populations with very low levels of gene diversity toward the northern ends of their ranges, probably due to founder effect accompanying recent colonization. The presence of several populations fixed 122 for one allele at many loci has the effect of increasing estimated population differentiation (GgT) and total gene diversity ( HT), which is exactly the pattern seen. Thus, atypical values for the two dioecious species are likely due to historical, rather than ecological or reproductive, factors.
The gynomonoecious and gynodioecious species were typical mixed- mating, animal pollinated seed plants at both the species and population levels with regard to gene diversity (Figures 25 and 26). The gynodioecious species would have unusually high total diversity, but within-population diversity would be closer to the typical value, if P. ciliata (with its very low sample size)
were not considered. As for population differentiation (GgT; Figure 27),
Polygonella fimbriata has a very low value that makes the mean for gynomonoecious species unusually low, and P. macrophylla and especially P. ciliata have high values that make the mean GgT for the gynodioecious species unusually high. While there is no obvious reason why P. fimbriata should have a very low GgT, the high value for P. ciliata is explained by low sample size and that for P. macrophylla is probably due to the high level of biparental inbreeding (and perhaps self-pollination) and the small population sizes
(discussed in Chapter II) characteristic of this species, giving it a GgT quite typical for obligate selfers.
The mean HT for the hermaphroditic polygonellas was within the 95% confidence limits for mixed-mating, animal-pollinated seed plants, albeit at the low end, while the mean //g for these species was entirely typical of selfers
(Figures 25 and 26). Polygonella articulata has exceptionally low values, and P. myriophylla high values, both for Hr and H a compared to mixed-mating, animal- pollinated seed plants, while P. americana is exceptionally low only in within- population diversity. Polygonella myriophylla is perennial, for which higher 123 gene diversities are predicted, but it is also geographically restricted, for which lower diversities are characteristic (see next section). The high diversity in this species may be partly due to historical factors and will be discussed further below and in the next chapter. Historical factors may have also had a role in the reduced levels of gene diversity in the two widespread hermaphrodites,
Polygonella articulata and P. americana , although it is difficult to rule out
mating-system effects. If these two species were obligate selfers, then one
would expect very low within-population diversity, which is indeed the case.
However, one would also predict high GST values, which are realized only in P. americana (Figure 27). It is important to keep in mind, however, that both Hr
and (?ST for P. articulata are minimum estimates, and could be much higher than reported here if the western populations are fixed for different alleles than their counterparts in the east. A low HT as well as Hs suggests colonization as a possible explanation, recent enough so that there has not been enough time for populations to become divergent.
Allozvme variation and geographic distribution
Predictions
Loveless & Hamrick (1984) pointed out that widespread species, in general, have better dispersal systems than do geographically restricted species.
Dispersal ability is tied with gene flow, and greater gene flow leads to larger parent-offspring distances (hence larger effective population sizes), lower levels of population differentiation, and less pronounced genetic drift. Widespread species should therefore maintain more diversity both at the population and species levels, and should display less population differentiation than their geographically restricted counterparts. However, it must be kept in mind that 124 the above only applies in situations where a species is not only widespread, but more or less continuously distributed with respect to its ability to disperse its genes. Thus, a species that has somehow managed to become widespread in the past, but now exists only in small, well-isolated, relict populations will of course suffer the depauperizing effects of genetic drift, and the variance in frequencies among populations will be greater than that expected in a "typical" widespread species. Another complicating factor is that along with greater dispersal ability comes the possibility that a species has rapidly colonized its present range from a relatively small number of populations. In this case, both diversity and differentiation among populations would be expected to be much less than usual for a widespread species, since founder effect plays an important role.
Observations
For seed plants in general, observation corresponds to expectation with respect to levels of gene diversity both within species (//T; Figure 28) and populations (//g; Figure 29); however, there were no significant differences among geographic distribution categories for GgT (Figure 30). Widespread seed plants harbor significantly more total and intrapopulational gene diversity than do endemic seed plant species, with regionally and narrowly distributed species being intermediate in gene diversity. The reasons for the lack of significant differences in C?gT may be found in the alternate scenarios presented above for widespread species.
Karron (1987), in an effort to avoid the problems associated with grouping together unrelated taxa often studied in different laboratories, compared genetic variation between restricted and widespread congeners and 125 came to the same basic conclusion: . . geographically restricted species exhibit significantly lower levels of genetic polymorphism than do the widespread
[congeneric] taxa.” Karron noted that historical factors add an important element of uncertainty to predictions of levels of genetic diversity based on extent of geographic distribution. Some endemics may be low in gene diversity due to severe genetic bottlenecks in the recent past, as may have been the case for Pinus torreyana (Ledig & Conkle 1983). Widespread species can also show low total gene diversity as the result of genetic bottlenecks (e.g., Pinus resinosa:
A llendorf et al. 1982; C ritchfield 1984; Fowler & Morris 1977). Endemics with moderate amounts of gene diversity are more difficult to explain (e.g.,
Capsicum cardenasii: McLeod et al. 1983, Gaura demareei: Gottlieb & Pilz 1976,
Layia discoidea'. G ottlieb et al. 1985, and Pinus longaeva: Hiebert & Hamrick
1983).
The relationship between gene diversity levels in Polygonella species and extent of geographic distribution is somewhat counterintuitive. The narrow endemics and regionally distributed species of the genus have higher levels of both total (//T; Figure 28) and within-population (//g; Figure 29) gene diversity than do the two species with the most widespread distributions. The six endemic species have high HT and Hs values compared to typical values for endemic seed plants, being more characteristic of narrowly distributed or regional seed plant species (as classified by Hamrick & Godt 1989). This observation remains accurate if Polygonella ciliata is not considered due to its low sample size. Of the six endemic polygonellas, only P. basiramia and P. parksii have <7ST values that would be considered normal for seed plant endemics (Figure 30). Polygonella macrophylla and P. ciliata have exceptionally high <7st values (probably for the reasons already discussed) and P. myriophylla 126 and P. fimbriata have quite low <7gT values. Low population differentiation in endemics such as P. myriophylla and P. fimbriata could be due to high levels of gene flow among the sampled populations, which as a consequence of being a geographically restricted species are closer geographically than sampled populations of more widespread species such as P. americana, which has a very high Cg r
Those polygonellas that I have classified as regionally distributed species, P. robusta (Florida peninsula), P. polygama and P. gracilis (southeastern
United States), have a higher average gene diversity than either the endemics or the widespread species. Intrapopulational diversity in these three species is typical for narrowly-distributed ( sensu Hamrick & Godt 1989) seed plant species, but total gene diversity is relatively high (more typical of widespread seed plants). (?ST values for P. polygama and P. gracilis are high, probably due to the presence of recently founded populations in both of these species, as discussed above.
The two widespread Polygonella species, P. articulata and P. americana, are thus the anomaly. If these two species are omitted, the relationship between levels of gene diversity (at both the species and population levels) and geographic distribution is very much what would be predicted. Even though
Hr for P. articulata may be in actuality much higher than the value reported here, the low Hs is still very unusual for a widespread species. Polygonella americana has the lowest values for both Hr and Hs of the entire genus, except for P. ciliata.
Possible reasons for the low levels of gene diversity in the two widespread species have been given above: 1) the species was formerly widespread but now exists as small, isolated relict populations suffering the 127 depauperizing effects of genetic drift; 2) the species has spread, from a small number of founding individuals, over its present range in the recent past, and is thus depauperate as the result of founder effect. The first explanation is most applicable to Polygonella americana , a widespread species with a relatively poor dispersal mechanism that does not appear capable of effecting a significant amount of migration among the small, isolated populations that are extant. This species occupies dune fields on the high plains of northwestern
Texas and northeastern New Mexico that represent eolean sediments deposited toward the end of the Pleistocene (Holliday 1990). During that period, high winds blew recently-uncovered glacial sediment over much of the sparsely- vegetated North American continent (Sutcliffe 1985:20). Such winds could have dispersed seeds of species from the deep south distances that would never have been possible otherwise given the dispersal system of the species. This scenario, though highly speculative, explains how a species without an obvious dispersal mechanism (other than gravity) could become dispersed over such wide expanses. Another hypothesis is that the species’ habitat, once widespread for a long period of time, has now become much reduced as the result of the changing climate following the Pleistocene glaciations, and P. americana only remains in places where its habitat still exists. These two scenarios are not mutually exclusive and could both apply to P. americana.
The second reason for unexpectedly low gene diversity levels in widespread species, recent colonization of a large area from a small number of founding individuals, applies best to Polygonella articulata, although is potentially applicable to P. americana as well. Polygonella articulata is distributed in the northern United States, extending south of the latitude of
Columbus, Ohio, only along the east coast; its southernmost population is in 128 southeastern Virginia (Figure 3). Although its low gene diversity is reported for the first time here, its lack of morphological variation attracted the attention of Horton (1963) who first suggested that this species might have recently recolonized its present range following the retreat of the Laurentide
Ice Sheet. In fact, almost all populations of P. articulata would necessarily have to be younger than about 14,000 years, as the land they occupy was covered with ice before that time. Recent recolonization explains not only the low intrapopulational gene diversity (founder effect) but also the low total diversity in the New England populations of this species, since the amount of time since colonization began may not have been long enough for significant population divergence. One would expect more of what diversity does exist to be distributed among populations (higher GgT) if the low levels of diversity were due to high rates of self-fertilization. This hypothesis relating extensive recolonization to the amount and apportionment of gene diversity in a species is the topic of the next chapter.
Summary
This study focused on estimating gene diversity in the eleven species of the flowering plant genus Polygonella at both the species (//T) and population
(//g) levels and comparing those estimates both with expected results and with values typical for seed plants. Although the species varied considerably,
Polygonella was found to have generally lower gene diversity at both levels, and more of that diversity was apportioned among populations in Polygonella compared to seed plants. As predicted, perennial Polygonella species had higher
Hr and Hs values than annuals, however the perennial species had on average more diversity among populations (higher GgT) than the annuals, a result 129 contrary both to prediction and to the typical condition for seed plants. Total gene diversity in dioecious Polygonella species was higher on average than in hermaphrodites, with species having gynodioecious and gynomonoecious breeding systems falling in between the two extremes. The Hs and (?ST values obtained for Polygonella have less obvious relationships to breeding system and indicate that the hermaphroditic species of Polygonella may comprise both highly selfing and predominantly outcrossing species. Contrary both to prediction and to data from seed plants in general, the widepread species of
Polygonella have the least gene diversity at both the species and population levels, while species with intermediate geographic distribution sizes have the highest. The endemic species have intermediate values for Hr and //g. An explanation of this phenomenon probably lies in the colonization history of the two widespread species. One of the two species appears to be depauperate because of genetic drift in small populations long isolated from each other.
The other species apparently spread quickly and recently into previously glaciated areas and thus its low diversity can be attributed both to founder effect (on Hs) and lack of time for divergence among populations (on //T). 130
L it e r a t u r e C ited
A llendorf , F. W., K nudsen , K. L., and Blake , G. M. 1982. Frequencies of null alleles at enzyme loci in natural populations of ponderosa and red pine. Genetics 100: 497-504.
Brow n , A. H. D., and Weir, B. S. 1983. Measuring genetic variability in plant populations. Pp. 219-329 in: T anksley , S. D., and O rton , T. J. (eds.), Isozymes in plant genetics and breeding. Part A. Elsevier, Amsterdam.
C ra w fo rd , D. J. 1983. Phylogenetic and systematic inferences from electrophoretic studies. Pp. 257-287 in: T anksley , S. D., and O rton , T. J. (eds.), Isozymes in plant genetics and breeding. Part A. Elsevier, Amsterdam.
C ra w fo rd , D. J. 1990. Plant molecular systematics: macromolecular approaches. John Wiley & Sons, New York.
C ritch field , W. B. 1984. Impact of the Pleistocene on the genetic structure of North American conifers. Pp. 70-118 in: L a n ner , R. M. (ed.), Proceedings of the eighth North American forest biology workshop. Logan, Utah.
F lorkin , M, and St o tz , E. H. (eds.) 1965. Comprehensive biochemistry. 13. Enzyme nomenclature. Elsevier Publishing Company, New York.
F ow ler , D. P., and M orris , R. W. 1977. Genetic diversity in red pine: evidence for low genic heterozygosity. Canadian Journal of Forest Research 7: 343- 347.
G o ttlieb , L. D. 1981. Gene number in species of Astereae that have different chromosome numbers. Proceedings of the National Academy of Sciences USA 78: 3726-3729.
G o ttlieb , L. D., a n d P ilz, G. 1976. Genetic sim ilarity between Gaura longiflora and its obligately outcrossing derivative G. demareei. Systematic Botany 1: 181-187.
G o ttlieb , L. D., Warw ick , S. I., and F ord , V. S. 1985. Morphological and electrophoretic divergence between Layia discoidea and L. glandulosa. Systematic Botany 10: 484-495.
H a m rick , J. L., and G odt , M J. W. 1989. Allozyme diversity in plant species. Pp. 43-63 in: Brow n , A. H. D., C legg , M T., K a h ler , A. L., and Weir, B. S. (eds.), Plant population genetics, breeding and genetic resources. Sinauer Associates, Inc., Sunderland, Massachusetts. 131
H a m rick , J. L., L inh a rt , Y. B., a n d Mitto n , J. B. 1979. Relationships between life history characteristics and electrophoretically-detectable genetic variation in plants. Annual Review of Ecology and Systematics 10: 173- 200.
H a m rick , J. L., M it t o n , Y. B., and J. B. L inh a rt . 1981. Levels of genetic variation in trees: Influence of life history characteristics. Pp. 35-41 in: C onkle , M. T . (ed.), Isozymes of North American forest trees and forest insects. Pacific Southwest Forest and Range Experiment Station, Berkeley, California.
H ie b e r t , R. D., a n d H amrick , J. L. 1983. Patterns and levels of genetic variation in Great Basin bristlecone pine, Pinus longaeva. Evolution 37: 302-310.
H olliday , V. T. 1990. Soils and landscape evolution of eolian plains: the Southern High Plains of Texas and New Mexico. Geomorphology 3: 489- 515.
H o rto n , J. H. 1963. A taxonomic revision of Polygonella (Polygonaceae). Brittonia 15: 177-203.
K a r r o n , J. D. 1987. A comparison of levels of genetic polymorphism and self compatibility in geographically restricted and widespread congeners. Evolutionary Ecololgy 1: 47-58.
L e d ig , F. T., and C onkle , M. T. 1983. Gene diversity and genetic structure in a narrow endemic, Torrey pine (Pinus torreyana Parry ex. Carr). Evolution 37: 79-85.
L e w is, P., and Whitk u s , R. 1989. GENESTAT for microcomputers. ASPT Newsletter 2: 15-16.
L oveless , M. D., and H amrick , J. L. 1984. Ecological determ inants of genetic structure in plant populations. Annual Review o f Ecology and Systematics 15: 65-95.
M cL eo d , ML J., G u ttm a n , S. I., E sh b au g h , W. H., and Rayle, R. E. 1983. An electrophoretic study of evolution in Capsicum (Solanaceae). Evolution 37: 562-574.
M endenhall , W., and Scheaffer , R. L. 1973. Mathematical statistics with applications. Duxbury Press, North Scituate, Massachusetts.
N e i, M. 1973. Analysis of gene diversity in subdivided populations. Proceedings o f the National Academy o f Science USA 70: 3321-3323.
N ei, M. 1987. Molecular evolutionary genetics. Columbia University Press, New York. 132
Soltis , D. E., H aufler , C. H., D arrow , D. C., a n d G astony , G. J. 1983. Starch gel electrophoresis of ferns: a compilation of grinding buffers, gel and electrode buffers, and staining schedules. American Fern Journal 73: 9-27.
Su tcliffe , A. J. 1985. On the track of ice age mammals. Harvard University Press, Cambridge, Massachusetts.
Werth, C. R. 1985. Implementing an isozyme laboratory at a field station. Virginia Journal of Science 36: 53-76.
Wrig h t , S. 1940. Breeding structure of populations in relation to speciation. American Naturalist 74: 232-248.
Wrig h t , S. 1943. Isolation-by-distance. Genetics 28: 114-138. 133
Table 9. Population name, state, county, number of loci sampled (L), and mean number of individuals sampled per locus (N) in the following format: Name (S t a t e : County) [L, N].
Polygonella fimbriata (4 populations). Claxton (G eorgia : Evans Co.) [14, 23.2]; Reidsville (G eorgia : Tattnall Co.) [12, 7.8]; Fitzgerald (G eorgia : Ben Hill Co.) [13, 27.7]; Tifton (G eorgia : Irw in Co.) [13, 15.8].
Polygonella robusta (8 populations). Sopchoppy (F lorida : Franklin Co.) [12, 8.3]; Bronson (F lorida : Levy Co.) [9, 2.3]; Radio Tower (F lo rida : M anatee Co.) [10, 25.7]; Disney (F lorida : Orange Co.) [10, 9.1]; Frontage Road (F lorida : Orange Co.) [10, 19.3]; Northside Nursery (F lorida : St. Lucie Co.) [10, 14.6]; Ft. Pierce (F lorida : St. Lucie Co.) [10, 9.5]; N. Bch. Cswy. (F lorida : St. Lucie Co.) [8, 7.9].
Polygonella articulata (10 populations). Omer (M ichigan : Arenac Co.) [15, 8.5]; Great Sand Bay (M ichigan : Keweenaw Co.) [7, 20.3]; Juneau (Wisconsin : Juneau Co.) [14, 24.9]; Essex (V erm ont : Chittenden Co.) [15, 23.1]; Randolph (N ew H am pshire : C oos C o .) [17, 25.3]; Fryeburg (M aine : O xford Co.) [11, 30.0]; Sebago Lake S. (M aine : Cumberland Co.) [15, 21.9]; Sebago Lake N. (Ma in e : Cumberland Co.) [12, 25.7]; Hampton (N ew H ampshire : Rockingham Co.) [14, 19.0]; Yarmouth (Massachusetts : Barnstable Co.) [12, 25.0].
Polygonella parksii (4 populations). Pleasanton (T exas : Atascosa Co.) [13, 21.8]; Seguin (T exas : Guadalupe Co.) [12, 20.3]; Hilltop Lakes (T exas : Leon Co.) [12, 24.8]; Rockdale (T exas : Burleson Co.) [15, 25.7].
Polygonella americana (8 populations). Oasis (N ew M ex ico : Roosevelt Co.) [15, 18.5]; Muleshoe (N ew Mexico : Roosevelt Co.) [11, 1.9]; B attiest (O klahoma : M cCurtain Co.) [14, 18.9]; Malvern (A rkansas : Hot Springs Co.) [14, 15.8]; McDade (T exas : Bastrop Co.) [11, 2.1]; Wrens (G eorgia : Jefferson Co.) [15, 3.8]; Aiken (South C arolina : Aiken Co.) [11, 22.1]; Columbia (South C arolina : Richmond Co.) [14, 22.2].
Polygonella myriophylla (4 populations). Gun Club (F l o r id a : Orange Co.) [8, 24.6]; Frostproof (F lorida : Polk Co.) [6, 20.3); Lake Ridge (F lorida : Highlands Co.) [10, 8.1]; Sun’N’Lake (F lorida : Highlands Co.) [5, 24.2].
Polygone 11a macrophylla (6 populations). Royal B luff (F lorida : Franklin Co.) [10, 39.9]; Royal Dune (F lorida : Franklin Co.) [10, 16.8]; Panama City (F lorida : Bay Co.) [10, 26.7]; Gray ton Bch. (F lorida : Walton Co.) [8, 17.0]; Destin (F lorida : Okaloosa Co.) [9, 14.9]; Gulf Shores (A labama : Baldwin Co.) [10, 10.2]. 134
Table 9 (continued)
Polygonella polygama (14 populations). P. polygama var. polygama : Aransas NWR (T exas : Aransas Co.) [11, 8.1]; Gulf Shores (A labama : Baldwin Co.) [7, 8.7]; Disney (F lorida : Orange Co.) [9, 5.0]; Beacon Hill (F lorida : G ulf Co.) [11, 6.7]; Sun’N Lake (F lorida : Highlands Co.) [6, 3.0]; Royal Dune (F lorida : Franklin Co.) [8, 3.5]; S tuart (F lorida : M artin Co.) [10, 5.0]; Carrabelle (F lorida : Franklin Co.) [7, 9.7]. P. polygama var. brachystachya: Marco Is. (F lorida : Collier Co.) [11, 9.4], P. polygama var. croomii: Jerome (N orth Carolina : Cumberland Co.) [11, 5.0]; White O ak (N orth C arolina : Bladen Co.) [12, 19.9]; Burgaw (N orth Carolina : Pender Co.) [11, 5.6]; Sugarloaf Mtn. (South C arolina : Chesterfield Co.) [11, 4.8]; Oak P ark (G eorg ia : Emanuel Co.) [11, 20.6].
Polygonella gracilis (11 populations). Oak Park (G eorgia : Emanuel Co.) [16, 23.8]; McRae (G eo rg ia : Telfair Co.) [15, 16.0]; Fitzgerald (G eorg ia : Ben Hill Co.) [9, 10.4]; Crestview (F lorida : Okaloosa Co.) [14, 9.6]; Bronson (F lorida : Levy Co.) [14, 10.8]; Vero Bch. (F lo rida : Indian River Co.) [15, 17.1]; G ulf Bch. (A labama : Baldwin Co.) [15, 12.5]; Sopchoppy (F lorida : Franklin Co.) [9, 2.9]; Royal Dune (F lorida : Franklin Co.) [12, 1.0]; Tampa (F lorida : Hillborough Co.) [14, 1.9]; Sun’N Lake (F lorida : Highlands Co.) [9, 1.0].
Polygonella ciliata (2 populations). Radio Tower (F lorida : M anatee Co.) [12, 4.3]; Frontage Road (F lorida : Orange Co.) [12, 4.0],
Polygonella basiramia (2 populations). Lake Annie (F lorida : Highlands Co.) [12, 17.0]; Sun’N Lake (F lorida : Highlands Co.) [12, 5.2]. 135
Table 10. Sample sizes and gene diversity statistics for the eleven species of Polygonella.
/■* ftb Species Pops. Indivs. Loci h t * " s * ST
P. fimbriata 4 18.6 13.0 0.0909 0.0703 0.0227 P. robusta S 12.1 9.9 0.1583 0.1128 0.2872 P. articulata 10 22.4 13.2 0.0203 0.0156 0.2288 P. parksii 4 23.2 13.0 0.1475 0.0964 0.3464 P. americana 8 13.2 13.1 0.0909 0.0098 0.8923 P. myriophylla 4 19.3 7.3 0.1789 0.1760 0.0164 P. macrophylla 6 15.6 9.5 0.1901 0.0854 0.5509 P. polygama 14 8.2 9.7 0.1798 0.0943 0.4753 P. gracilis 11 9.7 12.9 0.2208 0.0807 0.6347 P. ciliata 2 4.2 12.0 0.0483 0.0063 0.8687 P. basiramia 2 11.1 12.0 0.1090 0.0854 0.2165
Means 6.6 14.3 11.4 0.1304 0.0757 0.4127c aNot unbiased for sample site or number of populations; mean taken over monomorphic as well as polymorphic loci. Calculated from the means of and Hg for each species. cCalculated from the mean and Hg over all species. Figure 21. Total (//T) and intrapopulational ( Hs) gene diversity and coefficient of gene differentiation (<7ST) in Polygonella compared to seed plants.
136 .05 .to .1 5 JO .25 i—i—i—i—|—i—m —i—|—i i i i—|—r i i i —|—i—i—i—i—|—r
Sood Plants H 0 .1 4 9
Dleots 0 .1 3 6
I ■ i i i a rt eil ama baa par rob mvrmac pra fim pot
.0 5 .10 .15 .20 .25 i — r r i i— |— i—r—i—i—|— i—i—i—r I I "~'f I "
Sttd H Plants 0 .1 1 3
Dieots 0 .0 9 6
n i cll^ a rt f im /b a s pol par rob a me pro mac
0.1 0 .2 0 3 0 .4______0 3 ______0 .6______0 7______0 3 ______0 3 ______1 3 I I I I | I I I'l [ T l"l I | I I I l~j I' 1111111 ii 1111111111111111
Seed G Plant ST 0.22
Dicots 0 .2 7
rob par ell ame
Figure 21 Figure 22. Total gene diversity (//T) in Polygonella compared to seed plants, classified by life span.
138 139
i — i—i—i—r
Htrbeeaeus short-livad Annuals parannialf 0.161 ^ T 0 .1 1 6 0 .1 7 7
Veady lany- Life Span Wvad perennials
perennial
p o l^ m o c
Figure 22 Figure 23. Gene diversity within populations ( Hs) in Polygonella compared to seed plants, classified by life span.
140 141
0 .05 .tO .15 .20 25 “ 1----1----1 I 1 I I----1- | - | | | | -|—J I I I I "| I I I I | I
Htrbactous Voody H s *hort-Hv»d lony-Hvtd p*rtnni«1s ““ p*r«rm1»ls Life Span 0.0 9 6 0 .1 4 9 Annuls 0.105
Figure 23 Figure 24. Coefficient of gene differentiation (<7SX) in Polygonella compared to seed plants, classified by life span.
142 143
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 11 111 11 11 | 11111 11 11111 11111 11 "| 11111 i n it i n r | i r i r
□ □ CZH gst Woody Herbaceous Annuals long-lived short-lived „ , c , I ifa e n * n perennials perennials 0 357 L ,' e 5 P & n 0.076 0.233
perennial
Figure 24 Figure 25. Total gene diversity (//T) in Polygonella compared to seed plants, classified by breeding system.
144 145
.05 .10 .15 SO .25 i i i r 1— i— i— i— i— |— i— i— i— i— f— i— i— i— i— |— i— i— i— i— |— T
Salfars 0 .1 2 4
ht Mlxad- Animal 0.120 Outer .-Vlnd -ab Breeding 0 .1 6 2 Outor .-Animal Systems 0 .1 6 7 Mtxad-Vind 0 .1 9 4
hormep h rodltlc 1 i art ame myr
mm gynomonoecious3 fim rob
wr gynodioecious 3 ell bas par mac
dioecious gra DOl
Figure 25 Figure 26. Gene diversity within populations ( Hs) in Polygonella compared to seed plants, classified by breeding system.
146 147
0 .05 .10 .15 2 0 2 9 I I I I | I I 1 "" I | ~T I "I r | '" I ~T |" l | |-"| -|.... T | |-
Mixed-Vind 0 .1 9 8 Hs Breeding Outer .-Vind Outer 0 .1 4 8 Systems Animal M ixed- Animal 0 124 0 .0 9 0 ■cd
Seifert 0.074
hermaphroditic i i eme ert
SSSjSS-1 gynomoitoecloue
gunodloeclous
mac por bos
dioecious
gra pol
Figure 26 Figure 27. Coefficient of gene differentiation (CgT) in Polygonella compared to seed plants, classified by breeding system.
148 149
I I I I I 11 I I | I I I I | 1 1 I I 1 I I I I | i I I I | I Outcros* animal 5*1 fed 0.100 10 19 7 0 .5 1 0 | 0.216 wind** 0 9 Breeding Systems
hermaphroditic
gunomonoecious
gynodioecious
dioecious
Figure 27 Figure 28. Total gene diversity (/JT) in Polygonella compared to seed plants, classified by extent of geographic distribution.
150 151
.05 .10 .1 5 2 0 2 5 1" 1 i 1 | 1 1 1 • 1
R tfio n il V M tip r u d
0 .1 5 0 0 2 0 2 *"*T 0 .1 3 7 Geographic N «rrov
Distrbution Endtmic 0 .0 9 6
endemic
flm bas par myr moc
region*!
rob pol
widespread
Figure 28 Figure 29. Gene diversity within populations (//§) in Polygonella compared to seed plants, classified by extent of geographic distribution.
152 153
0 .0 5 .1 0 .1 5 2 0 25 i — i—i—i—i—r I" I " I—I I I I I I "I I l- i— i—i—i—|—r
H e Endemic Rcgtcnel Widespread
0 .0 6 3 0 .1 1 8 0 .1 5 9 0 .1 0 5 Geographic N c r r c v l distribution
endemic 1
c il flm bas par myr mac
regional
gra pol rob
widespread
ame art
Figure 29 Figure 30. Coefficient of gene differentiation (CgT) in Polygonella compared to seed plants, classified by extent of geographic distribution.
154 155
0 0 1 0.2 0.3 0.4 0.3 0.6 0.7 0.S 0.9 1.0 I I >T|~n II I I I IT I I I I I I I I I I I I I n~TT I i i p 'ITI I I I I I I’ IT I I
narrow «ST 0.242 Geographic region. 0.216 Distribution widespr. 0.210
endemic
regional
widespread
Figure 30 CHAPTER IV
CORRELATION OF GENE DIVERSITY WITH LATITUDE IN POLYGONELLA (POLYGONACEAE): TESTING AN HYPOTHESIS INVOLVING HISTORICAL FACTORS
I ntroduction
Much recent attention has focused on the identification of factors associated with differences among plant species in the amount and apportionment of genetic variation (Brown 1979; Gottlieb 1981; Hamrick &
Godt 1989; Hamrick et al. 1981; K arron 1987; Loveless & Hamrick 1984). The investigation of such associations is vital to efforts at conserving plant genetic resources; reasonably accurate predictive models allow both identification of species most genetically depauperate (and thus in need of protection) and estimation of the proportion of gene diversity distributed among rather than within populations.
Surveys of the plant genetic literature by Hamrick and colleagues, the most recent and inclusive of which was Hamrick & Godt (1989), identified several ecological, morphological, cytological and taxonomical features that are associated with differences in gene diversity. Levels of gene diversity within plant populations are strongly associated with: 1) the size of the geographic range (widespread vs. restricted); 2) breeding system (primarily outcrossing, mixed mating, or primarily selfing); 3) life form (annual vs. perennial); and 4) taxonomic status (gymnosperm, monocot, or dicot) (Hamrick & Godt 1989).
Differentiation among populations, however, is most strongly associated with
156 157 features that determine the extent to which a species disperses its genes, such as breeding system and seed dispersal mechanism (Hamrick & Godt 1989; Loveless
& Hamrick 1984). These broad-scale surveys necessarily concentrate on intrinsic attributes of organisms and do not incorporate historical factors, even though many individual studies rely heavily on explanations involving genetic bottlenecks accompanying founder events and/or genetic drift (e.g., Ledig &
Conkle 1983; Loveless & Hamrick 1988; Schwaegerle & Schaal 1979; Soltis 1982).
Estimates of the amount of variation in gene diversity explained by such models are usually less than 50% (Holsinger 1990) and often even lower for specific measures of diversity (e.g., 28% for population level diversity in
Hamrick & Godt 1989). Two reasons for this are: 1) error incurred in the measurement of gene diversity; 2) some variables correlated with levels of gene diversity were not included in the model.
The problem of measurement error is not trivial, since many electrophoretic studies conducted on plant subjects are hampered by the interference of secondary compounds (Kephart 1990) or simply low levels of enzyme activity. The number of enzyme loci scorable in studies of animal species is often quite large: 121 in Homo sapiens (Nei & Roychoudhury 1982);
49 in Alligator mississippiensis (Gartside et al. 1977); 47 in Acinonyx jubatus
(O’Brien et al. 1983); 46 in Drosophila pseudoobscura (Fuerst et al. 1977); 40 in
Mus muscnlus (Selander et al. 1969); 29 in Procyon lotor (Hamilton & Kennedy
1987). In constrast, the mean number of loci scored in 653 studies involving plants was only 16.5 (Hamrick & Godt 1989) and very few studies of plants report data for more than 25 loci; the 59 loci reported by Ledig & Conkle
(1983) was exceptional. This is unfortunate, since the largest component (by far) of the sampling variance in gene diversity (the m/erlocus component) can 158
be reduced only by increasing the number of loci (not the number of
individuals) sampled per population (Nei 1987, p. 180).
Because models used in predicting levels of gene diversity incorporate
only a few variables, there almost certainly exist some variables correlated with
diversity not included in the model. Comparisons involving species that are not
particularly closely related can add many unknowns to an analysis. As pointed
out by Karron (1987), investigations of associations of various traits of
organisms with gene diversity are much more meaningful when congeneric
species are compared using the same set of gene loci in the same laboratory.
Since genera are probably seldom polyphyletic groups, comparisons of congeners
provide the most constrol possible over unwanted species differences. Using
congeners also eliminates the related problem of determining whether or not
species "A" is more genetically diverse than species "B" simply because species
"A" inherited a more diverse gene pool from its ancester. Several examples
exist of geographically restricted species that have higher total genetic
variation than unrelated widespread species; however, it is difficult to
determine the significance of such a difference. For example, the proportion
of polymorphic loci in the geographically restricted Limnanthes vinculans is
41.2% (Kesseli & Jain 1984), whereas it is 0% in the unrelated widespread
species Lisianlhus skinneri (Sytsma & Schaal 1985). More helpful would be a
comparison in which a restricted species was more diverse than a widespread congener, because fewer assumptions must be made about negligible effects of additional (or unknown) species differences.
There is little doubt that unknown historical factors affecting individual populations of a species add much (seemingly random) variation to measurements of gene diversity; one would have to know (quite precisely) the 159 history of each population of a species, especially information about minimum population sizes, in order to account for such variation. Much about the past distribution of a species becomes available with a good fossil record; this type of information is invaluable in explanations of unusually low gene diversity
(e.g., Ledig & Conkle 1983). In some cases, it is possible to extrapolate from one population, about which much is known concerning past historical events, to other populations showing similar levels of gene diversity (e.g., Schwaegerle &
Schaal 1979).
A major historical event, affecting many species in a large area, may aid in the interpretation of some of the residual variation in gene diversity. One of the best examples of this was in a recent study of European populations of
Norway Spruce (Picea abies) utilizing both allozyme and morphological data
(Lagercratz & Ryman 1990). The similar patterns found for both gene diversity and morphology in European Picea abies were consistent with expectations based on the locations of Pleistocene refugia and reinvasion history predicted from pollen data. Lagercrantz & Ryman noted that central European populations were genetically depauperate, and attributed this to genetic bottlenecks associated with restricted population sizes while in refugia during the last glaciation.
Studies such as that by Lagercrantz & Ryman providing historical explanations of patterns of variation within a single species are important contributions to plant conservation efforts. The explanation of the effects of historical events on genetic variation among species presents an even greater challenge because of the complications posed by morphological and ecological species differences; however, the need for such studies is no less important. 160
Aims of this study
This study considered electrophoretic variation in soluble enzymes
among the eleven closely-related species of the North American plant genus
Polygonella in an attempt at incorporating both ecological and historical factors
into a predictive model of gene diversity. The hypothesis was that some of the
variation not explained by the usual suite of life-history/ecological traits might
be explained by the large-scale migrations known to have occurred for at least
some widespread North American plant species during the past 18,000 years.
Latitude was used as a rough measure of this "migration effect" since, all other
things being equal, northern populations were expected to have been founded
more recently and hence to be less genetically diverse (due to founder effects)
than southern conspecific populations. Multiple linear regression was used to
compare the association of latitude with intrapopulational gene diversity in the
presence of various attributes of the species.
M a t e r ia l s an d m e t h o d s
Collection of plant material and electrophoresis
Details of the grinding (extraction) buffers, gel and electrode buffers,
run times, voltage/current specifications, staining protocols, and scoring
procedures were explained in the Materials and Methods section of the previous chapter. Appendix A is a list of all sites at which Polygonella was found during the course of this project, along with information about associated species and dates visited. 161
Variables included in analyses
Of the traits that have been investigated in past surveys, only four were found to vary qualitatively among species of Polygonella. Three of those four were incorporated, together with latitude as a covariate, into a multiple linear regression model that was fitted to measures of gene diversity. Species traits used were: 1) breeding system (O=hermaphroditic. l=gynomonoecious,
2=gynodioecious, 3=dioecious); 2) life span (0=annual. l=perennial); and 3) relative size of geographic distribution (continuously variable). Seed dispersal mechanism was excluded because of its relationship with relative size of geographic distribution (see below).
Breeding system
The term breeding system is often used synonymously with mating system, but here a distinction is made in that mating system is taken to be a measure of the proportion of a plant’s total seed output derived from cross fertilization ( i.e., outcrossed seed), as opposed to the proportion derived from self-fertilization ( i.e., selfed seed). Breeding system here refers to the combination of floral types displayed by the individuals in a population of a species. The categories given above (i.e., hermaphroditic, gynomonoecious, etc.) are potentially related to the mating system in that hermaphroditic species are able to be completely selfing if they are self-compatible, dioecious species are obligate outcrossers, and the categories gynodioecious and gynomonoecious are likely to have mixed mating systems, although they could potentially be completely outcrossing (but not completely selfing since they possess some unisexual flowers). I have assumed by the scoring system used that the effects on gene diversity of these four breeding systems are ordered; this is tantamount 162 to equating breeding system categories to mating system categories, with gynomonoecious being considered as intermediate between hermaphroditic and gynodioecious, and gynodioecious intermediate between gynomonoecious and dioecious. Although I do not know the outcrossing rates of any except the dioecious species, there is evidence that at least one of the hermaphroditic species, Polygonella articulata, is self-compatible, a prerequisite for any correlation between breeding system and mating system.
Life span
The life span was considered perennial only if individuals exibited perenniality throughout the entire range of the species. Occasionally, individuals belonging to an ordinarily annual species live for two or three years if they are in the southern part of the species range (e.g., P. basiramia).
Polygonella robusta has been considered by other workers to be annual; however, the presence of persistent leaf bases on many individuals from throughout the range of the species led me to score this species as perennial.
Geographic distribution
Relative size of geographic distribution was measured by tracing (onto a piece of paper) a polygon just large enough to enclose all known localities of a species on a map of the United States and Canada, cutting out the tracing and weighing it to the nearest hundredth of a gram.
Seed dispersal
Seed dispersal in Polygonella is basically by gravity; however, two levels of adaptation to wind pollination have developed. The species Polygonella polygama, P. gracilis, P. basiramia, P. ciliata, and P. parksii have seeds that are 163 light enough to ride a short (usually less than 10 m) distance on the wind. One species however, Polygonella articulata, has a calyx that reflexes at maturity and acts as a parachute, enabling the seeds of this species to ride the wind for a much greater distance (perhaps as much as one km if conditions are adequate).
Because the extent of geographic distribution (which was included as a variable in the regression model) is a function of (among other things) seed dispersal ability, seed dispersal ability was no included in the regression model.
Measurement of gene diversity
Measure used at population level
The population gene diversity measure, h, described by Nei (1987, p. 178, eq. 8.4) was used to measure the amount of genetic diversity within populations.
This measure has been called expected heterozygosity by other workers, but the term gene diversity is preferred since it is more widely applicable, being simply the probability that two randomly chosen genes from a population are different
(Nei 1987, p. 177); the term expected heterozygosity only applies to random mating populations satisfying all the assumptions of Hardy-Weinberg equilibrium (Nei 1987, p. 178). This formulation of gene diversity is unbiased for sample size (Nei 1987, p. 178) and the average gene diversity across loci (H;
Nei 1987, p. 179, eq. 8.6) is unbiased for the number of loci, since the sample mean is an unbiased estimator of the population mean as long as the sampling of loci was random (Mendenhall & Scheaffer 1973, p. 268). H was also preferred over observed heterozygosity, since observed heterozygosity is strongly associated with breeding system in many plants (e.g.. Brown &
Albrecht 1980; Levin 1978; Schoen 1982a, 1982b) and does not take into account 164 an important component of genetic variation, the number of alleles at a locus, in highly selfing species.
Measure used at species level
Gene diversity estimate used at the level of a species was Hv the total gene diversity of Nei (1973:3322, eq. 8), unbiased for both sample size and number of populations sampled according to Nei & Chesser 1983:258, eq. 16).
The measure reflecting average population-level gene diversity was Hs (Nei
1973:3322, eq. 8), unbiased for sample size (Nei & Chesser 1983:258, eq. 15). Hs is a mean across populations and thus is unbiased with respect to the number of populations sampled as long as they represent independent samples of all populations of the species.
Analyses performed and data used
Statistical analyses were performed using the PC version of the SAS
(SAS Institute Inc. 1985) on an IBM Personal Computer equipped with an Intel
80386 microprocessor. Multiple Linear Regression was performed using the
SAS regression procedure REG and PROC CORR was used to obtain correlations of gene diversity estimates with latitude. Unbiased estimates of total (//T) and intrapopulational ( Hs) gene diversity were computed using the option "Gene diversity analysis: Unbiased for sample size and population number" of GeneStat-PC (Lewis & Whitkus 1989), version 3.2.
The data set consisted of HT and H s values, as well as measures of the variables G (relative size of geographic distribution), F (floral system
[^breeding system]), D (duration [=life span]), and MLAT (mean latitude), for each species, giving a total of 11 observations and 6 variables. 165
R e s u l t s
Gene diversity ( H) was estimated and latitude determined for a total of
74 populations representing all eleven species of Polygonella (Table 11). Total
gene diversity (Hr) and gene diversity within populations ( Hs) was estimated
and mean latitude calculated for each of the eleven species (Table 12).
Both Ht (r = -0.647; P = 0.0315; Figure 31a) and Hs (r - -0.535; P -
0.0899; Figure 31b) w ere strongly negatively correlated with mean latitude. In
addition, evidence for within-species variation in latitude-related gene diversity
was evident for two species and one pair of closely-related species. The mean
unbiased gene diversity for three Georgia populations of Polygonella gracilis
was 0.0253 while that of four populations in the Florida peninsula was almost
seven times higher (0.1755). The correlation between gene diversity (//) and
latitude for all eleven species of P. gracilis was significant (r = -0.743, P < 0.01;
Figure 32). Georgia and North Carolina populations of Polygonella polygama
have m ean gene diversity 0.0962, whereas Florida populations averaged 0.1488,
over 1.5 times greater. The third example is a species pair, Polygonella
Jimbriata/P. robusta. Once considered a single species, the major difference
between these two species is that Polygonella robusta is perennial and larger in
most features whereas P. fimbriata is annual. The mean gene diversity of the
Georgia populations of this Polygonella fimbriata/robusta complex is 0.0792
whereas the Florida populations average 0.1414. Analysis of covariance of the
37 populations making up these three taxa ( Polygonella gracilis, P. polygama, and the P. fimbriata/robusta complex) indicated that latitude (as the sole covariate) accounted for a significant proportion (r* = 0.164) of the variance of unbiased gene diversity (P = 0.013). When each taxon was evaluated independently using regression, only in Polygonella polygama did the model (H - 166
latitude + error) fail to account for a significant amount of the variation in unbiased gene diversity.
The regression model relating Hr to breeding system, geographic distribution, life span, and latitude accounted for 53.4% of the variation in HT among species (r2 adjusted for degrees of freedom used by the model) and
standardized regression coefficients identified breeding system as the best
predictor of //T, followed by life span, geographic distribution, and latitude,
respectively (Figure 33). The model accounted for a nearly significant amount of the total variation in HT (F = 3.865; P = 0.0691). Variation in Hs was much less predictable than that for Hr on the basis of the traits included in the model (F = 0.904; P = 0.5172); the amount of variation in Hs accounted for was effectively zero (the coefficient of determination, r2, adjusted for degrees of freedom, was -0.04).
D is c u s s io n
The primary question addressed by the multiple regression analysis was then "Is this reduction in gene diversity at both the species and population levels due to historical factors (genetic bottlenecks during the Pleistocene) or can it be explained adequately on the basis of certain species differences
(namely, life span, geographic distribution size, and breeding system)?".
Using historical events in predictive models
Event must affect many taxa in similar ways
For an historical event to be useful in a model of gene diversity, it must be of such a scope and nature so as to affect different species in much the same way. The Wisconsin glaciation, like the other glacial advances 167 characterizing the Pleistocene epoch, drastically and simultaneously affected the distribution of many plant species across North America and northern
Europe and Asia (Davis 1976). Below I discuss not only the wide-ranging effects of the Wisconsin glaciation and the present interglacial, but also the prediction that species (and populations within species) were affected in roughly similar ways in eastern North America.
The acme of the last interglacial period was about 125,000 years and the height of the Wisconsin glaciation about 18,000 years ago (Imbrie & Imbrie
1979:186). This last Pleistocene glaciation was accompanied by both an increase in ice coverage from 10% to 50% of the earth’s surface (between 30° N and 30°
S) and a decrease in sea level of more than 100 m (Sutcliff 1985, pp. 22-23).
Vast areas were covered with silt (loess) picked up from recently deglaciated and largely unvegetated land by strong winds blowing away from retreating continental glaciers, changing soil composition across much of North America
(Sutcliff 1985, p. 20).
Plant communities have been far from stable during the past 18,000 years, changing in species composition and extent of distribution (Davis 1976;
Delcourt & Delcourt 1981; Watts 1969). In addition to physically removing all vegetation from the land surface directly covered by the ice sheet, the presence of continental glaciers resulted in marked vegetational changes, with an open spruce woodland in the midwest (Webb 1981) and a wide (100 km) belt of tundra across central New York State and Pennsylvania (Maxwell & Davis
1972).
Both an extensive migration of northern North American plant species into the south (Watts 1969) and the subsequent Holocene recolonization of northern areas from southeastern or southwestern refugia during the past 168
10.000 years (Davis 1976) have been well documented from pollen deposition records. Such characteristically northern species as Pinus banksiana, P. resinosa,
P. strobus, Tsuga canadensis and Fagus grandifolia all migrated rapidly northward following the retreat of the Laurentide ice sheet (Davis 1976).
Interestingly, some species characteristic of certain dry, sandy habitats in the deep south apparently survived the glacial period in situ, perhaps even with expanded ranges compared to the present time (Delcourt & Delcourt 1981); examples include Ceratiola and Polygonella of the Sand Pine Scrub vegetation, today restricted primarily to the Florida peninsula (Delcourt & Delcourt 1981;
Watts 1975). In fact, the only areas in North America having a relatively constant flora during the late-Quaternary were west-central Mexico and the
Gulf Coastal Plain south of 33° N, including peninsular Florida (Delcourt &
Delcourt 1983).
Predictions about gene diversity
For North American plant species that migrated south at the onset of the
Wisonsin glacial and north again during the present interglacial, the greater the latitude of a population the more likely that population did not survive the glacial and was founded recently. In the case of a population presently situated on land formerly covered by ice, a maximum age can be formulated for the population. Populations now occupying areas at the position of the southernmost edge of the Laurentide ice sheet cannot be older than about
15.000 years (Davis 1976).
A loss of gene diversity would be expected to accompany a migration of the scale demonstrated for several North American tree species in the Holocene.
A better understanding of this prediction is facilitated by an example using a 169 typical northerly species (say, Fagus grandifolia), working out the steps involved in a large-scale plant migration. At the onset of the Wisconsin glacial period, the climate cooled and made previously unfavorable sites to the south of the distributional range of the species favorable. New populations founded to the south of the species’ range would have been depauperate relative to more northerly populations due to founder effect: not all of the alleles in the ancestral population would likely be represented in the founding individuals.
Once the climate cooled sufficiently, the most northerly populations became extinct, taking with them any alleles not represented in the newly-founded southern populations. During the relatively long glacial period (approximately
90,000 years), a certain amount of diversity was regained by mutation. Gene diversity was lost again during the northward migration that occurred following the retreat of the Laurentide ice sheet at the close of the Pleistocene.
Thus, at the present time we would expect species with northerly distributions to be genetically depauperate relative to species having southerly distributions, all other things being equal. Species differing by traits themselves expected to influence gene diversity may complicate the prediction somewhat, as would species that are not closely related.
The prediction above is also strongly dependent on the species having undergone a large-scale migration over the past few thousand years, and thus is more appropriate for species tending to have a more northerly (> 33° N) interglacial distribution. Species whose ranges during interglacial periods are entirely southern may not have been displaced by the climatic changes accompanying glacial periods. Pollen evidence indicates that Ceratiola ericoides 170 and Polygonella robusta1 inhabited the same locality near Lake Placid, Florida, continuously from about 37,000 years B.P. to the present; thus, at least these two species are known to have survived in situ the cooler climate of the glacial period. Gene diversity in these populations is expected to be greater than that in either newly-founded conspecific populations or populations-of a related, widespread, northern species that does not differ from it by any characteristics affecting gene diversity.
Gene diversity patterns in Polveonella
At the species level, latitude was the least effective predictor of total gene diversity2: breeding system, geographic distribution, and life span, in that order, were the best predictors. Thus, the hypothesis that the northerly- distributed species of Polygonella have less diversity than southerly species because of the migration and founder effect associated with the Wisconsin glaciation was not supported by the regression analysis. It is important however to identify reasons why these results may be misleading. First, there was enough uncertainty in predictions based on the regression model that the model did not explain a significant amount (5% level) of the variation in HT This uncertainty is mostly due to the low sample size of 11; had there been 25 or 30 species in Polygonella for which data could be collected, the model would almost certainly have explained a significant amount of the variance in HT
1 This species is listed as Polygonella fimbriata in Watts (1975). The variety of P. fimbriata was not given, but one can assume it was P. fimbriata var. robusta, since the other variety (P. fimbriata var. fimbriata) is presently restricted to Georgia; P. fimbriata var. robusta was recently elevated to specific status by Nesom & Bates (1984). 2 Since virtually none of the diversity within populations ( Hs) was able to be explained by the variables used in the model, only the total gene diversity (//T) will be discussed. 171
Second, while variation among species was not obviously more related to latitude than to the other traits in the model, variation in gene diversity within certain Polygonella species was strongly correlated with latitude. This is a secondary prediction of the migration/extinction hypothesis outlined above for species having a latitudinal range extending both north and south of about 33
N latitude. Within a species, the complicating influences of breeding system, life span, and dispersal capability are not a factor as they are in interspecific comparisons. Regression analysis is likely to be "confused" by coincidental combinations of factors such as are found in Polygonella. For example, even if migration/extinction was entirely responsible for the relatively low diversity in northern Polygonella species such as P. articulata and P. americana, regression analysis would have difficulty identifying this fact since both species are hermaphroditic (which, of the four breeding systems in the genus, is the most likely to be the cause of lowered gene diversity) and the most northerly (P. articulata) is also annual (which is also associated with lower diversity). Had the most northerly species in Polygonella been dioecious perennials and the most southerly annual hermaphrodites, then regression analysis would have had no trouble attributing the observed gene diversities differences to latitude. Third, it is notable that the standardized regression coefficient for the variable geographic distribution is negative. This means that, according to the regression equation, widespread species are predicted to have less diversity than geographically restricted species. This is both counterintuitive and the opposite of empirical results on hand for seed plants (Hamrick & Godt 1989; see also see
Chapter III). This is a further indication that the regression analysis may not constitute a valid test of the migration/extinction hypothesis. 172
It is quite possible that the effects of large scale migrations following the Wisconsin glaciation would be more apparent in other genera of plants.
Perhaps a more productive approach to testing this hypothesis would be to compare levels of diversity between related pairs of species that are very similar ecologically and morphologically with the exception that one has a northern distribution and the other a southern distribution. It is easy to find such pairs; there are many examples known of pairs of congeneric species in which one member is endemic to Florida and the other is either a Gulf Coastal
Plain species or is located even further north. Gentry (1986) found that, except for California and Hawaii, Florida was the richest in endemic plant species
(38S species) of all the states in the U.S. Many of these Florida endemics are either (1) species typical of and restricted to Sand Pine Scrub habitat (itself endemic to Florida), or (2) species that appear characteristic of northern climatic zones that probably either originated or migrated to Florida during the last glacial. Several endemics of the Sand Pine Scrub habitat on the Lake Wales
Ridge in central, peninsular Florida have northern, widespread congeners (Zona
& Judd 1986; Table 13). Examples of Florida endemics occupying cool, moist, forested habitats abound as well: Torreya taxi folia, Taxus floridana,
Rhododendron austrinum to mention a few (James 1961); the area in which these three species grow represents the southernmost extension of the ranges of several constituent species (Kurz 1939). One could then use nonparametric methods {e.g., Wilcoxon’s signed-ranks test) to assess whether differences are significantly related to latitude. Nonparametric tests were not possible in this study because of the violation of the assumption of independence between observations ( i.e., it would be necessary to used the same species in more than one paired comparison in order to obtain a sufficient sample size). 173
Future studies should also concentrate on obtaining data from more
populations (of fewer species, if necessary) as there is evidence that latitude is
strongly associated with gene diversity within certain species. The species in
which this effect was most pronounced were those with a wide latitudinal
distribution for which a relatively large number of populations were sampled
(e.g., Polygonella gracilis, P. polygama, and the P. fimbriata/robusta complex all
have populations in the Florida peninsula as well as in Georgia or the
Carolinas).
Summary
An hypothesis for the effect on gene diversity of the migrations imposed
by Pleistocene glaciations is proposed and tested using the eleven species of
Polygonella. Species with entirely northern (>33 N latitude) distributions are
expected to display less gene diversity than species with entirely southern
distributions. This is because northerly species were forced to migrate
southward during glacial maxima, and migration events such as these would
have involved repeated founder events (and extinction of many populations),
the net result being a genetic bottleneck for the species as a whole. Southerly
species, on the other hand, did not migrate and thus did not suffer population
extinction and recolonization to nearly the same extent, thus maintaining more
gene diversity. These predictions were complicated in Polygonella by the
differences in breeding system, life span, and geographic distribution size
(potentially related to dispersal ability), all of which by themselves are known
to influence levels of gene diversity. Thus, while multiple regression
implicated breeding system, geographic distribution, and life span as being
better predictors than latitude of total gene diversity, it was concluded for the 174 following reasons that the results for Polygonella alone are not sufficient to reject the hypothesis of influency by historical events. The two most northerly species of Polygonella coincidentally are also hermaphroditic, which, of the four breeding systems displayed by the species of Polygonella , is the most likely to lead to reduced gene diversity. Also confusing is that the regression model predicted that widespread species should show less total diversity than geographically restricted species, a prediction that is both counterintuitive and not borne out by surveys of gene diversity in seed plants. A better test of the predictions of the migration/extinction hypothesis would involve comparing pairs of closely-related species having similar life-history traits but differing greatly in their mean latitudes (one a northern species, the other southern). An even better test would be to compare northern to southern species having combinations of life history attributes that "stack the deck" against the hypothesis in that, on the basis of all life-history traits, the northern species would be predicted to have more diversity than the southern. 175
Literature Cited
Brown, A. H. D. 1979. Enzyme polymorphism in plant populations. Theoretical Population Biology 15: 1-42.
B r o w n , A . H . D ., a n d A l b r e c h t, L . 1980. Variable outcrossing and the genetic structure of predominantly self-pollinated species. Journal o f Theoretical Biology 82: 591-606.
D a v is , M. B. 1976. Pleistocene biogeography of temperate deciduous forests. Geoscience and Man 13: 13-26.
D e l c o u r t , P. A., a n d D e l c o u r t , H. R. 1981. Vegetation maps for eastern North America: 40,000 yr. B.P. to the present. Pp. 123-165 in: R o m a n s , R. C. (ed.), Geobotany II. Plenum, New York.
D e l c o u r t , P. A., a n d D e l c o u r t , H. R. 1983. Late-quaternary vegetational dynamics and community stability reconsidered. Quaternary Research 19: 265-271.
F u e r s t , P. A., C h a k r a b o r t y , R., a n d Nei, M. 1977. Statistical studies on protein polymorphism in natural populations. I. Distribution of single locus heterozygosity. Genetics 86: 455-483.
G a r t s id e , D . F ., D e s s a u e r , H. C., a n d J o a n e n , T . 1977. Genetic homozygosity in an ancient reptile ( Alligator mississippiensis). Biochemical Genetics 15: 655-663.
G e n t r y , A. H. 1986. Endemism in tropical versus temperate plant communities. Pp. 153-181 in: S o u l e , M. E . (ed.), Conservation biology, the science of scarcity and diversity , Sinauer Associates, Inc., Sunderland, Massachusetts.
G o t t l ie b , L. D. 1981. Electrophoretic evidence and plant populations. Progress in Phytochemistry 7: 1-46.
H a m il t o n , M . J., a n d K e n n e d y , M . L . 1987. Genic variability in the raccoon Procyon lotor. American Midland Naturalist 118: 266-274.
H a m r ic k , J. L., M it t o n , J. B., a n d L in h a r t , Y. B. 1981. Levels of genetic variation in trees: Influence of life history characteristics. Pp. 35-41 in: C o n k l e , M . T . (ed.), Isozymes of North American forest trees and forest insects, Pacific Southwest Forest and Range Experiment Station, Berkeley, California.
H a m r ic k , J. L., a n d G o d t , M. J. W. 1989. Allozyme diversity in plant species. Pp. 43-63 in: B r o w n , A. H. D., C l e g g , M. T., K a h l e r , A. L., a n d We ir , B. S. (eds.), Plant population genetics, breeding and genetic resources. Sinauer Associates, Inc., Sunderland, Massachusetts. 176
H o l s in g e r , K. E . 1990. Conservation of genetic diversity in rare plants: Principles and prospects. Abstract: ICSEB IV. Fourth International Congress of Systematic and Evolutionary Biology, University of Maryland and the Smithsonian Institution, College Park, Maryland. 1-7 July, 1990, p. 255.
I m b r ie , J., a n d I m b r ie , K. P. 1979. Ice ages: solving the mystery. H arvard University Press, Cambridge, Massachusetts.
J a m e s , C. W. 1961. Endemism in Florida. Brittonia 13: 225-244.
K u r z , H. 1939. Torreya west of the Apalachicola River. Proceedings o f the Florida Academy 3: 66-77.
K a r r o n , J. D. 1987. A comparison of levels of genetic polymorphism and self- compatibility in geographically restricted and widespread plant congeners. Evolutionary Ecololgy 1: 47-58.
K e s s e l i, R . V ., a n d J a in , S. K . 1984. New variation and biosystematic patterns detected by allozyme and morphological comparisons in Limnanthes s e c t. Reflexae (Limnanthaceae). Plant Systematics and Evolution 147: 133-165.
K e p h a r t , S. R. 1990. Starch gel electrophoresis of plant isozymes: A comparative analysis of techniques. American Journal o f Botany 77: 693- 712.
L a g e r c r a n t z , U., a n d R y m a n , N. 1990. Genetic structure of Norway Spruce {Picea abies): concordance of morphological and allozymic variation. Evolution 44: 38-53.
L e d ig , F. T., a n d C o n k l e , M. T. 1983. Gene diversity and genetic structure in a narrow endemic, Torrey Pine (Pinus torreyana Parry ex Carr.). Evolution 37: 79-85.
L e v in , D. A. 1978. Genetic variation in annual Phlox: Self-compatible versus self-incompatible species. Evolution 32: 245-263.
L e w is , P., a n d Wh it k u s , R. 1989. GENESTAT for microcomputers. ASPT Newsletter 2: 15-16.
L o v e l e s s , M. D., a n d H a m r ic k , J. L. 1984. Ecological determinants of genetic structure in plant populations. Annual Review of Ecology and Systematics 15: 65-95.
L o v e l e s s , M. D., a n d H a m r ic k , J. L. 1988. Genetic organization and evolutionary history in two North American species of Cirsium. Evolution 42: 254-265.
M a x w e l l , J. A., a n d D a v is , M. B. 1972. Pollen evidence of Pleistocene and Holocene vegetation on the Allegheny Plateau, Maryland. Quaternary Research 2: 506-530. 177
M e n d e n h a l l , W., a n d Sc h e a f f e r , R. L. 1973. Mathematical statistics with applications. Duxbury Press, North Scituate, Massachusetts.
N e i, M. 1973. Analysis of gene diversity in subdivided populations. Proceedings of the National Academy of Science USA 70: 3321-3323.
Nei, M. 1987. Molecular evolutionary genetics. Columbia University Press, New York.
N e i, M., and C h e s s e r, R. K. 1983. Estimation of fixation indices and gene diversities. Annals o f Human Genettics 47: 253-259.
N ei, M., a n d R oychoudhury , A. K. 1982. Genetic relationship and evolution of human races. Evolutionary Biology 14: 1-59.
Nesom, G. L., a n d B a te s, V . M. 1984. Reevaluation of intraspecific taxonomy in Polygonella (Polygonaceae). Brittonia 36: 37-44.
O’Brien, S. J., W ildt, D. E., Goldman, D., M e rrill, C. R., and B u s h , M. 1983. The cheetah is depauperate in genetic variation. Science 221: 460-462.
SAS I n s t it u t e I n c . 1985. SAS User’s guide: Statistics , version 5 edition. SAS Institute, Cary, NC.
S c h o e n , D. J. 1982a. The breeding system of Gilia achilleifolia: Variation in floral characteristics and outcrossing rate. Evolution 36: 352-360.
S c h o e n , D. J. 1982b. G enetic variability and the breeding system of Gilia achillei folia. Evolution 36: 361-370.
S c h w a e g e r l e , K. E., and Schaal, B. A. 1979. Genetic variability and founder effect in the pitcher plant Sarracenia purpurea L. Evolution 33: 1210-1218.
S e l a n d e r , R . K ., H u n g , W . G ., a nd Y a n g , S. Y . 1969. Protein polymorphism and genic heterozygosity in two European subspecies of the house mouse. Evolution 23: 379-390.
Soltis , D. E. 1982. Allozyme variability in Sullivantia (Saxifragaceae). Systematic Botany 7: 26-34.
S u t c l if f , A. J. 1985. On the track of Ice Age mammals. Harvard University Press, Cambridge, Massachusetts.
S y t sm a , K.. J., a n d S c h a a l , B. A. 1985. Genetic variation, differentiation, and evolution in a species complex of tropical shrubs based on isozymic data. Evolution 39: 582-593.
Wa t t s , W. A. 1969. A pollen diagram from Mud Lake, Marion County, north- central Florida. Geological Society of America Bulletin 80: 631-642. 178
Wa t t s , W. A. 1975. A late Quaternary record of vegetation from Lake Annie, south-central Florida. Geology 3: 344-346.
We b b , T., III. 1981. The past 11,000 years of vegetational change in eastern North America. BioScience 31: 501-506.
Z o n a , S. Z., a n d J u d d , W. S. 1986. Sabal etonia (Palmae): Systematics, distribution, ecology, and comparisons to other Florida scrub endemics. Sida 11: 417-427. 179
Table 11. Data set for 74 populations comprising 11 species* (SPP) scored for unbiased gene diversity (H), and latitude (LAT).
OBS SPP* POPULATION Nb LOCI' H* LAT
1 FIM Tifton 15.80 13 0.0470 31.4550 2 FIM Fitzgerald 27.70 13 0.0975 31.7167 3 FIM Reidsville 7.80 12 0.0916 32.0933 4 FIM Claxton 23.20 14 0.0806 32.1617 5 ROB Sopchoppy 8.25 12 0.0596 30.0833 6 ROB Bronson 2.89 9 0.0742 29.4467 7 ROB Radio Tower 25.70 10 0.1640 27.5000 8 ROB Disney 9.10 10 0.1947 28.3333 9 ROB Frontage 19.30 10 0.2025 28.3333 10 ROB Northside 14.60 10 0.1841 27.0000 11 ROB Ft. Pierce 9.50 10 0.1687 27.0000 12 ROB N. Bch. Cswy. 7.88 8 0.0834 27.0000 13 ART Omer 8.47 15 0.0000 44.0467 14 ART Gr. Sandbay 20.30 7 0.0000 47.4150 15 ART Juneau 24.90 14 0.0170 43.9833 16 ART Essex Jet. 23.10 15 0.0000 44.4883 17 ART Randolph 25.30 17 0.0000 44.4700 18 ART Fryeburg 30.00 11 0.0000 44.0150 19 ART Sebago N. 25.70 12 0.0614 43.8583 20 ART Sebago S. 21.90 15 0.0607 43.8583 21 ART Hampton 19.00 14 0.0138 42.9417 22 ART Yarmouth 25.00 12 0.0000 41.6467 23 PAR Pleasanton 21.80 13 0.0359 28.9583 24 PAR Seguin 20.30 12 0.1114 29.5700 25 PAR Rockdale 25.70 15 0.0643 30.6567 26 PAR Hilltop Lake 24.80 12 0.0724 30.6667 27 AME Oasis SP 18.50 15 0.0023 34.4017 28 AME Muleshoe 1.91 11 0.0000 34.2233 29 AME Battiest 18.90 14 0.0209 33.8967 30 AME Malvern 15.80 14 0.0000 34.3633 31 AME McDade 2.09 11 0.0069 30.2867 32 AME Wrens 3.80 15 0.0000 33.4700 33 AME Aiken 22.10 11 0.0000 33.5600 34 AME Rest Area 1.00 11 0.0000 33.9050 35 AME Columbia 22.20 14 0.0306 33.9933 36 MYR Gun Club 24.60 8 0.0506 28.4167 37 MYR Frost Proof 20.30 6 0.0000 27.7433 38 MYR Lake Ridge 8.10 10 0.2593 27.2983 39 MYR Sun’N Lake 24.20 5 0.2028 27.2983 40 MAC R. B luff 39.90 10 0.1146 29.8517 41 MAC R. Dune 16.80 10 0.1700 29.8517 42 MAC Panama City 26.70 10 0.0177 30.2767 180
Table 11 (continued)
43 MAC Grayton Bch. 17.00 8 0.1486 30.2767 44 MAC Destin 14.90 9 0.0552 30.2767 45 MAC G ulf Shores 10.20 10 0.0520 30.2767 46 POL Marco Island 9.36 11 0.1818 25.9717 47 POL Aransas NWR 8.09 11 0.0560 27.9850 48 POL Gulf Shores 8.71 7 0.3188 30.2767 49 POL Disney 5.00 9 0.1407 28.3333 50 POL Beacon Hill 6.73 11 0.1588 29.9233 51 POL Sun’N Lake 3.00 6 0.1556 27.2983 52 POL R. Dune 3.50 8 0.1028 29.8517 53 POL Stuart 5.00 10 0.1178 27.1983 54 POL Carrabelle 9.71 7 0.0143 29.8517 55 CRO Jerome 5.00 11 0.0808 34.8350 56 CRO White Oak 19.90 12 0.0551 34.8350 57 CRO Burgaw 5.64 11 0.1815 34.5500 58 CRO Sugarloaf 4.82 11 0.1091 34.5717 59 CRO Oak Park 20.60 11 0.0546 32.3600 60 GRA Oak Park 23.80 16 0.0372 32.3600 61 GRA McRae 16.00 15 0.0388 32.0700 62 GRA Fitzgerald 10.40 9 0.0000 31.7167 63 GRA Crestview 9.57 14 0.0548 30.7633 64 GRA Bronson 10.80 14 0.2237 29.4467 65 GRA Vero Bch. 17.10 15 0.1488 27.6667 66 GRA G ulf Bch. 12.50 15 0.1433 30.2767 67 GRA Sopchoppy 2.89 9 0.0592 30.0833 68 GRA R. Dune 1.00 12 0.1667 29.8517 69 GRA Tampa 1.93 14 0.1071 27.9517 70 GRA Sun’N Lake 1.00 9 0.2222 27.2983 71 CIL Radio Tower 4.33 12 0.0138 27.5000 72 CIL Frontage 4.00 12 0.0000 28.3333 73 BAS Lake Annie 17.00 12 0.0946 27.2000 74 BAS Sun’N Lake 5.17 12 0.0858 27.2983 a P. fimbriata (FIM), P. robusta (ROB), P. articulata (ART), P. parksii (PAR), P. americana (AME), P. myriophylla (MYR), P. polygama var. polygama (POL), P. polygama var. croomii (CRO), P. macrophylla (MAC), P. gracilis (GRA), P. ciliata (CIL), P. basiramia (BAS) b Mean number of individuals scored per locus c Number of loci scored d Unbiased for sample size (N) 181
Table 12. Mean values for each species for total gene diversity HT, w ithin population gene diversity Hs, and latitude.
SPPa POPS Nb LOCIe LATd h t * HS Gg Lh B' ART 10 22.37 13.20 44.07 0.0214 0.0160 398 0 0 AME 9 11.81 12.89 33.57 0.1011 0.0113 255 1 0 FIM 4 18.62 13.00 31.86 0.0978 0.0735 6 0 1 POL 14 8.22 9.71 30.56 0.1870 0.1027 368 1 3 MAC 6 20.92 9.50 30.14 0.2126 0.0891 6 1 2 PAR 4 23.15 13.00 29.96 0.1658 0.1002 7 0 2 GRA 11 9.73 12.91 29.95 0.2390 0.1052 143 0 3 ROB 8 12.15 9.88 28.09 0.1649 0.1224 78 1 1 CIL 2 4.17 12.00 27.92 0.0902 0.0070 35 0 2 MYR 4 19.30 7.25 27.69 0.1897 0.1892 3 1 0 BAS 2 11.09 12.00 27.25 0.1325 0.0903 3 0 2 a See bottom of table 1 for species abbreviations b Mean number of individuals scored per locus per population c Mean number of loci scored per population d Mean latitude across all populations (POPS) of the species e Total gene diversity, unbiased for both sample size (N) and number of populations sampled (POPS); may be underestimated for ART since only the seven easternmost populations could be used fGene diversity within populations, unbiased for sample size (N) g Geographic distribution: value given is the weight of a paper representation of the distribution of each taxon in thousandths of one gram (see Materials and Methods). h Life span: annual (0), perennial (1). 1 Breeding system: hermaphroditic (0), gynomonoecious (1), gynodioecious (2), dioecious (3). 182
Table 13. Examples of species and congeneric species pairs that could provide valuable insight into the effect on gene diversity of large-scale northward plant migration following the Wisconsin glaciation in North America.
■ Widespread species whose ranges extend from Florida to New England or Canada. Chamaecyparis thyoides (L.) BSP.
■ Florida Sand Pine/Sclerophyllous Oak Scrub endemics with close ties to more widespread species {in curly brackets}. Sabal etonia Swingle ex Nash [S. palmetto (Walt.) Lodd. ex J. A. & J. H. Schultes} (Zona & Judd 1986) Asclepias curtissii A. Gray {A. purpurascens L.} (Woodson 1954) Chionanthus pygmaeus Small {C. virginicus L.) (Hardin 1974) Ilex opaca Aiton var. arenicola (Ashe) Ashe {/.opaca var. opaca } (Wunderlin 1982) Osmanthus megacarpa Small {O. americana (L.) Benth. & hook. f. ex A. Gray) (H ardin 1974) Persea humilis Nash (P. borbonia (L.) Spreng.) (Wofford 1973) Polygonella basiramia (Small) Nesom & Bates {P. gracilis (Nutt.) Meissn.) (Horton 1963) Polygonella myriophylla (Small) Horton (P. americana (Fisch. & Mey.) Small) (Horton 1963) Prunus geniculata Harper {P. angustifolia Marsh.) (Harper 1911) Quercus inopina ... {Q. myrtifolia Willd.) (Johnson & Abrahamson 1982)
■ Florida (±) endemics and congeneric northern species (closeness of relationship within the genus unclear at present). Liatris ohlingerae ... {£. cylindracea Michx.) Pinus clausa (Engelm.) Vasey. {P. banksiana Lamb.) Rhododendron austrinum ... {R . canadense (L.) BSP.)
■ Florida (±) endemics that are thought to be relict species because (a) they are from characteristically northern genera or (b) they were known to be much more widespread in the past from fossil records. Taxus floridana Nutt. (James 1961) Torreya taxi folia Am. (James 1961) Hartwrightia floridana A. Gray ex S. Wats. (James 1961) Leitneria floridana Chapm. (James 1961, Berry 1917, Cham berlain 1917) Figure 31. Scatter plots of gene diversity (ordinate) against mean latitude (abscissa) for the eleven species of Polygonella. A. Total gene diversity, H~, unbiased for both sample size and number of populations sampled. B. Witnin- population gene diversity, Hs, unbiased for sample size.
183 Gene Diversity (Ht) vs. Latitude
0.14
0.13
0.1
37 3 0 U * 7 M 41 4 3
Gene Diversity (Hs) vs. Latitude
0.10 0.10 0.17 0.10 0.13 0.14 0.13 0.13 0.11 0.1
O jOO
O jQO 0 j07
O jOO 0JQ3 0J04
O jQS 0 j03
O jOI 0 3 337 31 3 3 41 4 3
Figure 31 Figure 32. Scatter plot of gene diversity, H, unbiased for sample size, (ordinate) against latitude (abscissa) for the eleven populations of Polygonella gracilis.
185 Gene Diversity (H) vs. Latitude
o.ta 0.1 a o.u
0.12
0.1
OXB
0 j0 4
0X 3 0 2 7 2* 51 5 5
Figure 32 187
Total Gene Diversity
Dependent variable: HT
Sum of Mean Source DF Squares Square F Value Pr > F
Model 4 0.0292 0.0073 3.865 0.0691 Error 6 0.0113 0.0019 Total 10 0.0406
Standardized r2 = 0.7204 Variable Parameter Estimate A djusted-r2 = 0.5341
Breeding syst. 0.7134 Life span 0.6217 Geogr. distr. -0.4298 Mean latitude 0.1078
Gene Diversity Within Populations
Dependent variable: Hs
Sum of Mean Source DF Squares Square F Value Pr > F
Model 4 0.0111 0.0028 0.904 0.5172 Error 6 0.0185 0.0031 Total 10 0.0296
Standardized r2 = 0.3759 Variable Parameter Estimate Adjusted-r2 = -0.0401
Life span 0.3736 Geogr. distr. -0.2852 Mean latitude -0.2229 Breeding syst. 0.0715
Figure 33. ANOVA tables and standardized regression coefficients for total gene diversity (//T) and gene diversity within populations (//g) for regressions of gene diversity on the traits breeding system, life span, geographic distribution, and mean latitude in Polygonella. APPENDIX A
POLYGONELLA LOCALITIES VISITED DURING THE COURSE OF THIS STUDY
ABBREVIATIONS: Directions: e, east; w, west; n, north, s, south; se, southeast; ne, northeast; sw, southwest; nw, northwest; nnw, north-northwest; etc. Highways: I-, interstate; SR-, state route; CR-, county route; US-, United States highway; FM-, farm-to-market road (endemic to Texas). Distances: mi, mile; m, meter.
CONVENTIONS: [x @ y] signifies an intersection of two roads, x and y (e.g., [1-30 @ US-270] translates as "the intersection of Interstate 30 and U.S. highway 270);
NOTE: I have included only those collection numbers for which the plants were able to be identified at least to genus. The name inclosed in square brackets (or something very similar) is the name by which the population is referenced in the text.
ALABAMA: Baldwin Co. [Gulf Bch. SP] Intersection of SR-182 with an unmarked road within Guld Beach State Park. Area with much bare sand. Polygonella gracilis here is what Small called Delopyrum filiforme, with long, terete leaves. 6-May-1990 2471. Polygonella gracilis (Nutt.) Meisn.
ALABAMA: Baldwin Co. [Gulf Shores] Along both sides of SR-182, 0.85 mi e of [SR-182 @ SR-161], e of Gulf Shores. In waist-high oak scrub with frequent Rosemary vegetation dense. 17-Nov-1988 2396. Polygonella gracilis (Nutt.) Meisn. 2397. Polygonella polygama (Vent.) Engelm. & Gray 2398. Polygonella macrophylla Small 6-M ay-1990 2472. Polygonella macrophylla Small 2473. Polygonella polygama (Vent.) Engelm. & Gray
188 189
ARKANSAS: Hot Springs Co. [Malvern] From [1-30 @ US-270], go se (towards M alvern) 0.8 mi, then take a right and go 0.5 mi sw. Novaculite outcrops on the e bank of the Ouachita River under the SR-84 bridge (which is out at the present time). Altitude: 90 m. 25-Aug-1988 2201. Polygonella americana (Fisch. & Mey.) Small 2202. Vernonia angustifolia Michx. 2203. Panicum hians Ell. 2-May-1990 2434. Polygonella americana (Fisch. & Mey.) Small 2435. Sm ilax sp. 2436. Allium sp. 2437. Apocynum sp.
FLORIDA: Bay Co. [Hathaway Bridge] US-98 less than 0.1 mi w of [US-98 @ alt-US-98] about 1.7 mi w of w end of Hathaway Bridge at Panama City. 29-Oct-1988 2321. Polygonella polygama (Vent.) Engelm. & Gray 2322. Polygonella gracilis (Nutt.) Meisn.
FLORIDA: Bay Co. [Panama City] On w side of Powell Adams road 0.1 mi s of the intersection [Powell Adams Road @ US-98], which is 1.5 mi e of [SR-79 @ US-98] in Panama City Beach. 29-Oct-1988 2323. Polygonella macrophylla Small 30-Sep-1988 2431. Polygonella macrophylla Small
FLORIDA: Bay Co. [SR-386 @ US-98] Along dirt road paralleling US-98 4.3 mi nw of [US-98 <© SR-386] at the Gulf-Bay Co. line. Polygonella gracilis present. 29-Oct-1988 2320. Polygonella polygama (Vent.) Engelm. & Gray
FLORIDA: Collier Co. [Marco Is.] Marco Island, corner of Dogwood and SR-92, 2.2 mi e of [SR-92 @ SR- 953]. Quercus geminata, Rhus sp., Serenoa sp., Palafoxia sp. About an acre of coastal scrub (no pines) with dense layer of vegetation up to 1.5 m above the soil level. 9-Nov-1988 2350. Polygonella polygama (Vent.) Engelm. & Gray var. brachystachya (Meisn.) Wunderlin 2351. Palafoxia sp. 8-May-1990 2488. Polygonella polygama (Vent.) Engelm. & Gray var. brachystachya (Meisn.) Wunderlin 190
FLORIDA: Franklin Co. [Appalachicola] N side of US-98 about 21 mi e of Carrabelle Beach. 28-Oct-1988 2298. Polygonella robusta (Small) Nesom & Bates 2299. Calamintha coccinea (Nutt.) Benth. 2300. Polygonella polygama (Vent.) Engelm. & Gray 2301. Haplopappus divaricatus (Nutt.) Gray 2302. Smilax auriculata Walt.
FLORIDA: Franklin Co. [Carrabelle Bch.] N side of US-98 at Carrabelle Beach (across road from picnic tables and shower house facility). 28-Oct-1988 2303. Polygonella polygama (Vent.) Engelm. & Gray 30-Sep-1988 2422. Polygonella robusta (Small) Nesom & Bates 2423. Polygonella gracilis (Nutt.) Meisn. 2424. Polygonella polygama (Vent.) Engelm. & Gray
FLORIDA: Franklin Co. [Royal Bluff] Royal Bluff, Sand Pine-Sclerophylous Oak Scrub n of US-98 5.8 mi w of Carrabelle City Beach. Quercus geminata, Q. chapmanii, and Pinus clausa predominate. 28-Oct-1988 2304. Lupinus villosus Willd. 2305. Pityopsis graminifolia (Michx.) Nutt. 2306. Conradina canescens (T. & G.) Gray 2307. Polygonella gracilis (Nutt.) Meisn. 2308. Quercus myrtifolia Willd. 2309. Quercus geminata Small 2310. Gaylussacia frondosa (L.) T. & G. 2311. Polygonella macrophylla Small 30-Sep-1988 2428. Polygonella macrophylla Small
FLORIDA: Franklin Co. [Royal Dune] Sand ridge perpendicular to US-98 and Gulf Coast, e of Royal Bluff, 5.0 mi w of ssw end of bridge at Carrabelle. Burned about four years or more ago. Quercus myrtifolia, Q. chapmanii, Q. geminata, Smilax sp,, Lycania sp., Conradina sp., and Ceratiola ericoides predominate; several dead Pinus clausa. 28-Oct-1988 2312. Polygonella polygama (Vent.) Engelm. & Gray 2313. Polygonella macrophylla Small 30-Sep-1988 2425. Polygonella polygama (Vent.) Engelm. & Gray 2426. Polygonella macrophylla Small 2427. Polygonella gracilis (Nutt.) Meisn. 191
FLORIDA: Franklin Co. [Sopchoppy] Roadside along US-319 just n of [US-319 @ US-98], s of Sopchoppy (also s of Ochlockonee River State Park). 30-Sep-1989 2421. Polygonella robusta (Small) Nesom & Bates
FLORIDA: G ulf Co. [Beacon Hill] E side of US-98, 3.9 mi nw of [US-98 @ SR-71]and 5.7 mi se of [US-98 @ SR-386] (in Beacon Hill) at the Bay-Gulf county line. 28-Oct-1988 2314. Polygonella gracilis (Nutt.) Meisn. 2315. Polygonella polygama (Vent.) Engelm. & Gray 2316. Chrysoma pauciflosculosa (Michx.) Greene 2317. Conradina canescens (T. & G.) Gray 2318. Liatris provincialis G odfrey 2319. Paronychia erecta (Chapm.) Shinners 30-Sep-1988 2429. Polygonella polygama (Vent.) Engelm. & Gray 2430. Polygonella gracilis (Nutt.) Meisn.
FLORIDA: Highlands Co. [Lake Annie] Fire lane and adjoining scrub between w side of Lake Annie and boundary of the Archbold Biological Station. 10-Nov-1988 2352. Polygonella basiramia (Small) Nesom & Bates 7-May-1990 2481. Polygonella basiramia (Small) Nesom & Bates 2482. Vaccinium sp. 2484. Conradina sp.
FLORIDA: Highlands Co. [Palmetto Dr.] W side of US-27 and just n of Palmetto Drive in white sand. 5.5 mi n of the Lake Placid Tower; 5.75 mi n of [US-27 @ SR-621]. 27-Oct-1988 2296. Polygonella robusta (Small) Nesom & Bates 2297. Polygonella myriophylla (Small) Horton
FLORIDA: Highlands Co. [Sun’N Lake] W side of SR-29 4.6 mi nnw of [SR-29 @ SR-70] and 2.75 mi e of [SR-29 @ US-27] (se of Lake Placid near Sun’N’Lake Estates). Very small roadside scrub with a very healthy population (50 individuals maximum) of Polygonella myriophylla and P. basiramia (200-300 individuals. P. polygama and P. gracilis also present at this site in much smaller numbers. 6-Nov-1988 192
FLORIDA: Highlands Co. [Venus] County Road C-731, n side, 0.5 to 1.1 mi w of US-27 near Venus. Scrubby flatwoods with Slash Pine, Quercus myrtifolia, Q. inopina, Q. geminata, zAristida stricta, Paronychia sp., Serenoa repens, Palafoxia sp., Heterotheca sp., Polygonella gracilis, P. basiramia, and P. polygama. 9-Nov-1988 2348. Polygonella basiramia (Small) Nesom & Bates 2349. Polygonella polygama (Vent.) Engelm. & Gray
FLORIDA: Hillborough Co. [Fletcher @ Skipper] 0.37 mi n of Flethcer Ave, w of 30th. Street, and n of an appartment complex named Sun Pointe Lake. Between Fletcher and Skipper Avenue, nw of Univ. S. Florida campus. Long-leaf Pine, scrub oaks, Serenoa repens, typical sandhill vegetation. 8-Nov-1988 2341. Polygonella robusta (Small) Nesom & Bates 2342. Polygonella gracilis (Nutt.) Meisn. 2343. Quercus sp. 2344. Quercus sp. 8-May-1990 2492.
FLORIDA: Indian River Co. [Vero Bch. N] US-1 4.1 mi n of [US-1 SR-60] in Vero Beach. W side of the highway in an area apparently once scrub. Selaginella abundant but few other scrub indicators. 1 l-Nov-1988 2375. Polygonella gracilis (Nutt.) Meisn. 9-May-1990 2503. Polygonella gracilis (Nutt.) Meisn. 193
FLORIDA: Levy Co. [Bronson] E of Bronson along SR-339 4.8 mi, 7.3 mi, and 9.5 mi e of [Alt-US-27 @ SR-339]). Turkey oak scrub bordering highway, in places with quite a bit of bare sand. Polygonella gracilis here is what Small referred to as Delopyrum filiforme, with long, terete leaves. 17-Nov-1988 2381. Polygonella gracilis (Nutt.) Meisn. 2382. Polygonella robusta (Small) Nesom & Bates 2383. Polygonella gracilis (Nutt.) Meisn. 2384. Polygonella robusta (Small) Nesom & Bates 2385. Polygonella gracilis (Nutt.) Meisn. 2386. Polygonella robusta (Small) Nesom & Bates 2387. Aristida sp. 2388. Polygonella gracilis (Nutt.) Meisn. 2389. Polygonella gracilis (Nutt.) Meisn. 2390. Polygonella gracilis (Nutt.) Meisn. 2391. Hypericum sp. 2392. Aristida sp. 2393. Polygonella gracilis (Nutt.) Meisn. 2394. Polygonella robusta (Small) Nesom & Bates 6-May-1990 2480. Polygonella gracilis (Nutt.) Meisn.
FLORIDA: Manatee Co. [Radio Tower] Vacant lot 0.2 mi e of CR-675 on n side of Jennings Road (across from a radio tower) just s of [CR-675 @ CR-64]. 8-Nov-1988 2331. Polygonella robusta (Small) Nesom & Bates 2332. Polygonella ciliata Meisn. 7-May-1990 2485. Polygonella myriophylla (Small) Horton 2486. Polygonella polygama (Vent.) Engelm. & Gray 2487. Gaura angustifolia
FLORIDA: Martin Co. [Stuart] 5.1 mi s of [SR-76 @ US-1] sw of Stuart, along SR-76 on the w side of the road sw of jet SR-76 and Gaines Ave. Scrubby area with sandhill character, no sand pine but instead Long-leaf Pine; used as a dump. 12-Nov-1988 2356. Polygonella polygama (Vent.) Engelm. & Gray 2357. Liatris sp. 2360. Palafoxia sp. 2361. Schizachyrium sp. 2363. Calamintha sp. 2364. Chrysopsis sp. 2365. Vaccinium sp. 2366. Quercus sp. 2367. Juncus sp. 9-M ay-1990 2493. Polygonella polygama (Vent.) Engelm. & Gray 2494. Quercus chapmanii
FLORIDA: Okaloosa Co. [Crestview] 8.4 mi e of [I-10 @ SR-85] at Crestview. Westbound I-10 roadsides. Area of Turkey Oak/Long-leaf Pine/Holly but not much Wiregrass. 17-Nov-1988 2395. Polygonella gracilis (Nutt.) Meisn. 6-M ay-1990 2474. Polygonella gracilis (Nutt.) Meisn. 2476. Phlox sp. 2477. Clematis sp.
FLORIDA: Okaloosa Co. [Destin] N side of US-98 3.4 mi e of e end of bridge over Choctawhatchee Bay at Destin. Sand Pine Scrub community. 30-Sep-1989 2433. Polygonella macrophylla Small 6-May-1990 2478. Polygonella macrophylla Small
FLORIDA: Orange Co. [Disney] 0.4 mi n of US-192 along both sides of SR-545, and in a sandy area w of SR-545 being used as a dump. Extreme sw corner of Orange Co. 6-Nov-1988 2329. Polygonella polygama (Vent.) Engelm. & Gray 2330. Polygonella robusta (Small) Nesom & Bates 10-May-1990 2517. Polygonella polygama (Vent.) Engelm. & Gray 2518. Polygonella robusta (Small) Nesom & Bates 195
FLORIDA: Orange Co. [Frontage Rd.] Just se of [1-4 @ SR-535] s of Vineland. Go s on SR-535 0.25 mi and turn left on Vineland Road. Go 0.15 mi and Polygonella ciliata is bordering pond on the e side of the road in bare sand. P. polygama also present. 4-Nov-1988 2323. Polygonella ciliata Meisn. 9-May-1990 2504. Polygonella ciliata Meisn. 2505. Polygonella robusta (Small) Nesom & Bates 2506. Polygonella polygama (Vent.) Engelm. & Gray
FLORIDA: Orange Co. [Gun Club] Along Fenton Street 0.75 mi e of [Apopka Vineland Road @ Fenton Street], which is 2.0 mi n of [1-4 @ Winter Garden Vineland Road (SR- 535)]. Old growth Sand Pine Scrub, with a nearly closed canopy. Some Polygonella myriophylla growing in lawn of the Gun Club, saved from the mowers by its prostrate habit! 17-Nov-1988 2378. Polygonella myriophylla (Small) Horton 2379. Polygonella ciliata Meisn. 2380. Polygonella polygama (Vent.) Engelm. & Gray 9-May-1990 2507. Polygonella myriophylla (Small) Horton 2508. Pinus clausa
FLORIDA: Orange Co. [SR-595] Sandy margin of Pinus clausa scrub bordering SR-535 0.2 mi s of [1-4 @ SR-535]. 4-Nov-1988 2324. Polygonella robusta (Small) Nesom & Bates
FLORIDA: Pinellas Co. [McMullen Rd.] 0.17 m s of [McMullen Road @ Boyette Road] on e side of McMullen Road. Long-leaf Pine overstory, with Aristida, Lyconia, Serenoa repens, Balduina, Quercus virginiana, and Q. laurifolia. 8-Nov-1988 2334. Polygonella ciliata Meisn. 2335. Eryngium sp. 2336. Elephantopus sp. 2339. Liatris sp. 2340. Centaurea sp. 2345. Quercus sp. 2347. Quercus sp. 196
FLORIDA: Polk Co. [Avon Park Bombing Range] 0.25 mi ne of Polk-Highlands Co. line along e side of SR-64 e of Avon Park on the way to the Bombing Range. Polygonella basiramia abundant in the disturbed deep white sand between the scrub and the mown, grassy, highway right-of-way; P. polygama frequent but only inside and at the margin of the scrub itself. 11-Nov-1988 2353. Chrysopsis floridana
FLORIDA: Polk Co. [Frostproof] 1.6 mi w of US-27 on US-27A (Alt-27), s of FrostProof. Mature scrub with Pinus clausa, Quercus chapmanii, Q. myrtifolia, Q. geminata, Q. inopina, and Bonamia grandiflora. 6-Nov-1988 2325. Polygonella polygama (Vent.) Engelm. & Gray 2326. Polygonella myriophylla (Small) Horton 14-Nov-1988 2377. Polygonella basiramia (Small) Nesom & Bates
FLORIDA: Polk Co. [N. C. Hill Rd.] On w side of SR-64 across SR-64 from the beginning of N. C. Hill Road, which is 7.05 mi e of [SR-64 @ US-27] near Avon Park. 1 l-Nov-1988 2355. Polygonella polygama (Vent.) Engelm. & Gray
FLORIDA: St. Lucie Co. [Ft. Pierce] 0.25 mi w of SR-707 along CR-712 (n side). Large sandy area apparently created recently by bulldozer activity. 9-May-1990 2496. Polygonella robusta (Small) Nesom & Bates 1 l-Nov-1988
FLORIDA: St. Lucie Co. [N. Bch. Cswy.] N of Ft. Pierce, 1 mi s of St. Lucie; se of [US-1 @ N. Bch. Cswy.]. Area with a large amount of bare sand, surrounded by a busy commercial plaza; probably will not be long before something is built upon this site. 9-May-1990 2447. Polygonella robusta (Small) Nesom & Bates 2448. Gaura sp. 2449. 2450. 2451. ll-Nov-1988 197
FLORIDA: St. Lucie Co. [Northside Nursery] E side of US-1, vacant lot just s of a plant nursery (Northside Nursery), 9.1 mi s of 12th. St. (Vero Beach) and 10.2 mi s of [SR-60 @ US-1]. Sand pine/scrub hickory area with much bare white sand. 1 l-Nov-1988 2370. Polygonella ciliata Meisn. 2371. Polygonella robusta (Small) Nesom & Bates 2372. Cuscuta sp. 2374. Vinca sp. 9-May-1990 2502. Polygonella robusta (Small) Nesom & Bates
FLORIDA: Volusia Co. [Daytona Bch.] Exit ramp (southbound) of exit 88 on 1-95 near Daytona Beach. Area of white sand in nw corner of interchange, [1-95 @ SR-40] (n of SR-40 and w of 1-95). 23-Oct-1988 2295. Polygonella gracilis (Nutt.) Meisn.
FLORIDA: Walton Co. [Grayton Bch.] S of US-98 at the edge of Grayton Beach State Park along road leading e to Seagrove Beach. Nearly closed pine canopy. 30-Sep-1989 2432. Polygonella macrophylla Small
FLORIDA: Orange Co. [Laurel Ave.] From Haines City, take US-92 e, taking right on the Cypress Parkway. Go 9.7 mi, taking right onto Poinsiana. After 6 mi, turn right onto Laurel Ave. and go 1.25 mi. Site is sandy roadside. 6-Nov-1988 2328. Polygonella gracilis (Nutt.) Meisn.
GEORGIA: Ben Hill Co. [Fitzgerald] Along US-129 n of Fitzgerald and s of Queensland, just s of the community of Bowen’s Mill. Area of bare sand w of the road. 29-Sep-1989 2420. Polygonella fimbriata (Ell.) Horton 10-May-1990 2519. Polygonella gracilis (Nutt.) Meisn. 2520. Polygonella fimbriata (Ell.) Horton 198
GEORGIA: Emanuel Co. [Oak Park] 0.15 mi e of US-1 along road 0.4 mi s of where US-1 passes beneath 1-16. Turkey Oak, Laurel Oak, Ceratiola ericoides, Opuntia sp., Lycopodium appressum, and Polygonella polygama var. croomii predominate. 22-Oct-1988 2292. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2293. Polygonella gracilis (Nutt.) Meisn. 2294. Balduina uni flora Nutt. 29-Sep-1988 2416. Polygonella gracilis (Nutt.) Meisn. 2417. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 10-May-1990 2531. Gilia sp. 2532. Polygonella polygama (Vent.) Engelm. & Gray 2534. Quercus laevis
GEORGIA: Evans Co. [Claxton] 2.7 mi s of [US-25/301 @ US-280] in Claxton. Around entrance to Gospel Baptist Temple on the e side of US-25/301. 22-Oct-1988 29-Sep-1988 2418. Polygonella fimbriata (Ell.) Horton 10-May-1990 2528. Phlox sp. 2529. Polygonella fimbriata (Ell.) Horton
GEORGIA: Irwin Co. [Tifton] 0.3 mi n of Tift-Irwin Co. line along US-319 between Tifton and Ocilla. 10-May-1990 2414. Polygonella fimbriata (Ell.) Horton 2516. Plantago sp.
GEORGIA: Jefferson Co. [Wrens] 0.35 mi s of McDuffy Co. line along SR-304. E side of road in field of Andropogon under widely-spaced Long-leaf Pine. Turkey Oaks and Crataegus sp. also present. 22-Oct-1988 2289. Polygonella americana (Fisch. & Mey.) Small 2290. Andropogon sp. 29-Sep-1988 2415. Polygonella americana (Fisch. & Mey.) Small 10-May-1990 2540. Baptisia perfoliata (L.) R. Brown 2541. Polygonella americana (Fisch. & Mey.) Small 199
GEORGIA: Tattnall Co. [Reidsville] Roadside of US-280 where it crosses the Ohoopee River near Reisville. 10-May-1990 2525. Polygonella fimbriata (Ell.) Horton 2526. Polygonella polygama (Vent.) Engelm. & Gray
GEORGIA: Telfair Co. [McRae] Lake in Little Ocmulgee State Park, 0.7 mi w of US-441 n of McRae. 29-Sep-1989 2419. Polygonella gracilis (Nutt.) Meisn. 10-May-1990 2521. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2522. Asclepias humistrata Walter
MAINE: Cumberland Co. [Sebago Lake N] Roadside of US-302 at n end of Sebago Lake. 12-Aug-1989 2408. Polygonella articulata (L.) Meisn.
MAINE: Cumberland Co. [Sebago Lake S] 0.1 mi n of [SR-114 @ SR-35] at Sebago Lake. Between old RR tracks and shore of the lake at the public access. 12-Aug-1989 2409. Polygonella articulata (L.) Meisn.
MAINE: Oxford Co. [Fryeburg] Roadside along US-302 1.3 mi w of [US-302 @ SR-93], w of Bridgton. 12-Aug-1989 2407. Polygonella articulata (L.) Meisn.
MASSACHUSETTS: Barnstable Co. [Yarmouth] West Yarmouth a t [Mill Pond Road @ US-28]. 3l-Aug-1990 2561. Polygonella articulata (L.) Meisn. 2562. Hypericum gentianoides (L.) BSP. 2563. Chrysopsis falcata (Pursh) Ell. 2564. Mollugo verticillata L. 2565. Centaurea maculosa Lam. 2566. Trifolium arvense L. 2567. Lechea maritima Leggett. 2568. Solidago tenuifolia Pursh.
MICHIGAN: Alger Co. [Munising] Sand Point, Pictured Rocks National Lakeshore. 2.5 mi nne of highway H58 at Munising at end of road bordering Grand Island harbor on the e side. 30-Sep-1988 2259. Polygonella articulata (L.) Meisn. 200
MICHIGAN: Arenac Co. [Omer] 1.85 mi nw of US-23 at Omer (on N. Michigan Rd.), 0.7 mi nw of Omer Evergreen Cemetery, s of Rifle River. Oak-Jack Pine woods, no aspen. 28-Sep-1988 2249. Polygonella articulata (L.) Meisn.
MICHIGAN: Keweenaw Co. [Betc Grise] Outlet of Lac La Belle just n of the Bete Grise Light. 7.95 mi e of US-41 and 3.6 mi e of fork in road at the village of Lac La Belle. Altitude: 183 m. 1-O ct-1988 2260. Dianthus deltoides MICHIGAN: Keweenaw Co. [Great Sand Bay] Great Sand Bay, 4.6 mi ene of bridge over Eagle River along SR-26 (Sand Dunes Drive), s side of the road amongst Meram Grass on sand dunes. 1-Oct-1988 MICHIGAN: Montmorency Co. [Glen’s Market] Sandy field just s of Glen’s Market, just se of the intersection [SR-612 @ SR-489] in Lewiston. 29-Sep-1988 2258. Polygonella articulata (L.) Meisn. MICHIGAN: Oscoda Co. [Mio Au Sable School] Between football field and school bus depot at Mio Au Sable school on the w side of the town of Mio, n of SR-72. 29-Sep-1988 2250. Populus tremuloides NEW HAMPSHIRE: Coos Co. [Randolph] US-2 3.6 mi w of [US-2 @ SR-16] near Gorham near Mt. Washington; just w of Randolph Hill Road, in coarse sand along roadside. 10-Aug-1989 2406. Polygonella articulata (L.) Meisn. NEW HAMPSHIRE: Rockingham Co. [Hampton] From 1-95, go e on SR-51 and take exit for 1-1C; plants are along sandy berm of offramp. 12-Aug-1989 2410. Polygonella articulata (L.) Meisn. 201 NEW MEXICO: Roosevelt Co. [Muleshoe] 1.7 m s of FM-1760 along dirt road that lies atop the Texas-New Mexico state line. Old sand dune to the w of the road (not the more conspicuous bare-sand dunes to the e of the road). Altitude: 1218 m. 26-Aug-1988 2214. Aristida sp. 2215. Schizachyrium sp. 2216. Bouteloua sp. 2217. Prunus sp. 2221. Paronychia sp. 2222. Artemisia sp. 2223. Euphorbia sp. 3-May-1990 2444. Penstemon sp. 2445. Rhus sp. 2446. Polygonella americana (Fisch. & Mey.) Small NEW MEXICO: Roosevelt Co. [Oasis SP] Along SR-467 2.25 mi n of US-70 (take US-70 ne out of Portales and turn left onto SR-467 towards Oasis State Park). Altitude: 1185 m. 28-Aug-1988 2227. Polygonella americana (Fisch. & Mey.) Small 2229. Helianthus sp. 3-M ay-1990 2442. Prunus sp. NORTH CAROLINA: Bladen Co. [Jones Lake SP] 2.4 mi n of [SR-242 @ SR-53] along SR-242 in Jones Lake State Park. 28-Sep-1989 2413. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. NORTH CAROLINA: Bladen Co. [White Oak] SR-53 (e side) 3.8 mi s of Cumberland-Bladen Co. line. Sandy, recently- logged field of young Turkey Oaks and Long-leaf Pines. 20-Oct-1988 2276. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2277. Centaurea cyanus L. 28-Sep-1988 2412. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 11-M ay-1990 2557. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 202 NORTH CAROLINA: Cumberland Co. [Jerome] E side of SR-53, 1.25 mi N of Cumberland-Bladen Co. line. Turkey Oak- Long-leaf Pine open forest on white sand; stumps indicate logging in the past. Power line right-of-way. 20-0ct-1988 2266. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2267. Lycopodium appressum (Chapm.) Lloyd & Underwood 2268. Quercus laevis Walt. 2269. Quercus laurifolia Michx. 2270. Hypericum fasciculatum Lam. 2271. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2272. Eriocaulon decangulare L. 2274. Panicum sp. 2275. Andropogon sp. 28-Sep-1989 2411. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 11-May-1990 2558. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2559. Vaccineum sp. OKLAHOMA: McCurtain Co. [Battiest] From Battiest, go s on US-259, take a right on Weyerhaeuser service road 56000 (sign says 53000) and go 5.9 mi, take left fork and go 2.5 mi and park at Dale Bowen’s house. From there, walk rest of the way down to the Arkansas Crossing of the Glover River. Novaculite outcrops. Altitude: 199 m. 26-Aug-1988 2204. Polygonella americana (Fisch. & Mey.) Small 2205. Vernonia angustifolia Michx. 2206. Thelesperma trifidum (Poir.) Britt. 2207. Paronychia fastigiata (Raf.) Fern. 2208. Diodia teres Walt. 2-May-1990 2438. Erigeron sp. 2439. Polemonium sp. 2440. Valerianella sp. 2441. Penstemon sp. 203 SOUTH CAROLINA: Aiken Co. [Aiken] SR-19 3.0 mi s of [SR-19 @ 1-20], n of Aiken. W side of road across from Graves Auto Salvage. Quercus laevis, Rhus copallina, Aristida sp., Erigeron sp., Heterotheca sp., and Pinus taeda predominate. 22-Oct-1988 2287. Polygonella americana (Fisch. & Mey.) Small 2288. Nyssa? sp. II-M ay-1990 2542. Polygonella americana (Fisch. & Mey.) Small 2543. Silene sp. SOUTH CAROLINA: Chesterfield Co. [Patrick] 1.35 mi n of US-1 en route to Sugarloaf Mtn. along SR-109. W side of road in sandhill vegetation. Turkey Oak-Long-leaf Pine present but not old and not abundant; possibly clear cut in the past but no sign of stumps. Yellowish sand, Bluestem abundant. 21-Oct-1988 2278. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2279. Centaurea cyanus L. 2280. Andropogon scoparius Michx. 2281. Aristida tuberculosa Nutt. 2282. 2283. Hypericum gentianoides (L.) BSP. 2284. Heterotheca graminifolia (Michx.) Shinners 28-Sep-1988 2414. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. SOUTH CAROLINA: Chesterfield Co. [Sugarloaf Mtn.] Beside Scotch road leading to Sugarloaf Mtn. Go n 2.9 mi from US-1 along SR-109, turning right onto Scotch Road, then go 0.20 mi e. 21-Oct-1988 2285. Polygonella polygama (Vent.) Engelm. & Gray var. croomii (Chapm.) Fern. 2286. Panicum agrostoides Sprengel 1 l-May-1990 2550. Tradescantia sp. 2551. Silene sp. 2552. Panicum sp. 2554. Polygonella polygama (Vent.) Engelm. & Gray SOUTH CAROLINA: Richland Co. [Columbia] Roadside embankment beside overpass, along 1-20 in Columbia. 1 l-May-1990 2545. Polygonella americana (Fisch. & Mey.) Small 2547. Specularia sp. 2549. Rumex sp. 204 TEXAS: Aransas Co. [Aransaw NWR] Aransas National Wildlife Refuge, near parking area for Dagger Point Trail and along Dagger Point Trail in sandy Oak/Bay community. 20-Mar-1989 2399. Polygonella polygama (Vent.) Engelm. & Gray TEXAS: Atascosa Co. [Pleasanton] S of San Antonio, n of Pleasanton; 6.8 mi s of [FM-1604 @ US-281]. Along US-281 near a drainage underpass on the e side of the road among live oaks and hickories and in an old field on the s side of the gravel road heading w from US-281 less than 100 m from US-281. 30-Aug-1988 2232. Polygonella parksii Cory. 4-May-1990 2447. Linum sp. 2449. Chaetopappa imberbis (Gray) Nesom 2450. Paronychia sp. 2451. Phlox sp. 2452. Tradescantia sp. 2453. Delphinium sp. 2454. Gaillardia amblyodon Gay 2455. Brazoria sp. 2456. Acalypha sp. TEXAS: Bastrop Co. [McDade] 2.4 mi e of McDade on US-290. Forest margin on s side of highway and at service entrance to a transmitting tower which is at the top of an embankment sloping down on the n side of the road. 5.4 mi w of [US-290 @ SR-21] (s side of the road). Forest of Post Oak and Hickory. Altitude: 180 m. l-Sep-1988 2234. Polygonella americana (Fisch. & Mey.) Small 2236. Lechia sp. 2239. Juniperus sp. 4-May-1990 2458. Polygonella americana (Fisch. & Mey.) Small 2459. Penstemon sp. TEXAS: Burleson Co. [Rockdale] 5-May-1990 2460. Polygonella parksii Cory. 2461. Coreopsis sp. 2462. Castileja sp. 2463. Gaillardia sp. 205 TEXAS: Guadalupe Co. [Sequin] 0.7 m n of FM-1681 along fence row on e side o f SR-123 and on bare sand on the other (e) side of the fence. 31-Aug-1988 2233. Polygonella parksii Cory. 4-May-1990 2457. Polygonella parksii Cory. TEXAS: Leon Co. [Hilltop Lakes] Inside Hilltop Lakes Resort City. Go w on FM-3 8.7 mi from [FM-3 @ FM-39] in Normangee, then right into the resort (at the main gate). Take Hilltop Drive 1.9 mi, take left on dirt road going around Cherokee Lake; Site is 0.5 m i on right. 1-Sep-1988 2240. Polygonella parksii Cory. 2241. Eragrostis sp. 2242. Quercus sp. 2244. Cnidosculus stimulosus «;auths> 2245. Cassia sp. 2246. Lechia sp. 23-Mar-1989 2400. Polygonella parksii Cory. 5-May-1990 2464. Polygonella parksii Cory. 2465. Gaillardia sp. 2466. Coreopsis sp. 2469. Tradescantia sp. 2470. Phlox sp. VERMONT: Chittenden Co. [Essex] 0.6 mi w of [SR-2A @ Lamore Road] in Essex. Fred Dumar’s property. 2.7 mi n of [SR-2A @ CR-15]. Panicum, Comptonia, Cyperus, Quercus, and Rhus (2 spp.) present. 10-Aug-1989 2405. Polygonella articulata (L.) Meisn. WISCONSIN: Juneau Co. [Juneau] W side of SR-80, 0.9 mi n of [SR-80 @ 1-90/94] (nw corner of [SR-80 @ 30th. St. E.]). Among pine trees. 2-Oct-1988 2265. Polygonella articulata (L.) Meisn. APPENDIX B NEXUS DATA SET USED IN CHAPTER I Data set used in conjunction with PAUP to perform cladistic analyses described in Chapter I. The NEXUS format is a standardized cladistic program data format now being used by PAUP and MACLADE for data and assumption entry. The data is provided in this format here because it would make it possible to not only reconstruct the data set used but also the assumption sets (phylogenetic constraints, character exclusion sets, etc.) used, making possible a recreation of the analysis. 206 #NEXUS 'obovate_to_spatulate_(generally)1, 27 present absent, BEGIN DATA; 28 'erect/spreading/arching' 'deflexed/strongly_nodding' DIMENSIONS NTAX=34 NCHAR=54; 29 strongly_undulate straight_or_curved, 30 always_present very_rarely_present, UPolygonella/Duravia (Polygonaceae) data set of 54 characters] 31 1present_(at_least_onejpai r)1 absent, FORMAT MISSING=? GAP=- SYMBOLS* "012 3"; 32 ,present_(at_least_on_some_plants' absent, 33 'short_(0.9-2.4_[3.0]jnn)' STATELABELS 1 long_( [2.4]_2.5-4.7_[6.0] Jim )', 1 thickened_to_edge 'witl^thin.Jtyaline^im 1, 34 '1:1' 'about_2:1', 2 relatively_thick_and_opaque 35 'whitish/greenish/yellowish/pinki * dark_orange, 1m i th_th i n,_hyaIi ne_or_sIi gh11y_y', 36 'long_(0.4-1.0jnn>' 'short J0.1-0.2jm _to_sessile)', 3 persistent early_deciduous, 37 'longjO.S-O.Sjim)' 'short_(0.3-0.4>', 4 absent_or_depression_veryjx>orly strongly_developed, 38 ' long_(27-32_un)' 'short_(16-21_un)', 5 appressed fla rin g , 39 ,short_(1.6-2.6_lml), 1 long_(2.8-3.7_irm)', 6 present absent, 40 strong Heak_to_absent, 7 singlevascularbundle triplet_of_vascular_bundles, 41 absent present, 8 present absent, 42 present absent, 9 hermaphroditic gynomonoecious gynodioecious dioecious, 43 planar revolute_or_sharply_folded_downw, 10 absent p resen t, 44 smooth_to_mucronulate_or_apicula 11 'short_tubular-obdeltate' long_tubular, ' spi ne-1 ippedjjromi nently_i n_some', 12 cuneate_to_truncate auricutate, 45 p resen t absent, 13 'erect-appressed_to_somewhat_spre* reflexed, 46 entire erose_or_nith_linear_segments_no, 14 usually_absent present, 47 green white, 15 obovate 'narrowly_oblanceolate-oblong', 48 ■ long_C1-3jnn)' 'short_(0-0.9_iiin>', 16 'dentire_to_slightly_wavy-crisped\' deeply_fimbriate, 49 '1:1' '2:1', 17 basally_dilated gradually_widening_on_all_eight, 50 8 '3-5_(in_at_least_some_flowers)', 18 'smooth-margined1 Hithj»ir_of_projections_or_knob, 51 basal lyjJistinct basal ly_comate, 19 yellow_to_orange_or_pink usually_dark_red_to_blackish, 52 'not_thiekened,_hardened_or_persi• 20 absent present, ' thickened,_hardened_and_persiste', 21 smooth pebbled, 53 'ye11owish-brown_(sometimes_very_' pitch_black, 22 annual perennial, 54 'smooth-shiny' 'striate-pebbled1. 23 erect prostrate, 24 absent present, 25 absent p re se n t, 26 linear_to_narrowly_lanceolate terete CHARLABELS [36] style_length [11 leaf_apex [37] anther_thecae_length [2] [eafjn arg in s [38] 1po11en_gra i n_length_(average)1 [3] leaf_persistence [39] achene_length [4] f [anged_depress i on_ i n_rach i s [40] 1leaf_articulation_(be[ow_congest' [5] ocreola_position [41] bracteal_leaves_fused_basally_to [6] ocreal_awns [42] cuticle_on_lower_leaf_surface_st [7] ocreal_awn_composi t i on_if_awns_p [43] leaf_margins [8] b racteo les [44] leaf_apex [9] fIora[ jnorphoIogy [45] vei ns_or_ri bs_i n_ocrea[_setae_or [10] ftower_base_extended_i nto_a_prom [46] ocreae_margins [11] flower_base [47] margin_of_bracteal_leaves [12] outer_sepal_base_shape [48] pedicel_length [13] outer_sepal_pos i t i on [49] ' length_rat i o_of_mature_outer:i nn1 [14] transitional_sepal [50] fertile_stamens [15] se p a lsh a p e [51] sty[e_branches [16] sepaljnargins [52] base_of_sty[e_branches [17] imer_three_f i lament_bases [53] achene_color [18] iimer_three_f i laments [54] 'achene_surface_completely:1 [19] anther_thecae_eotor $ [20] achene_neck_prominently_extended [21] 'Behene_surface_(upper_1/5)' MATRIX [ [22] duration 1 2 3 4 5 ] [ [23] hab it 123456789012345678901234567890123456789012345678901234] [24] woodrays P._fimbriata [25] ,bundle_sheaths_of_sclerified,_pi 000000001101010110701000100001110010100001100000001010 [26] (e a fsh a p e P._robusta [27] conical_epidermal_celIs 000000001101010110001100100001111010000001100000001010 [28] fIora t jpos it i on_at_anthes i s P._articulata [29] anticl inalnal (s_of_sepat_epider 100111010110000001100000011100000011100001100000001010 [30] sepal_stomata P ._parksii [31] lateral_sepal_veins 000111012110000001000000111000000100000001100000001010 [32] * thickened,_green_sepal_micl^ib, P._americana [33] *sepal_length_(longest_mature_sep 100111010111100001000101111010001100001001100000001010 [34] ■ rat i o_i nner:outer_mature_sepaIs1 P.jnyriophylla [35] 'sepa l_coIor_(matur i ng_and_dry i ng 100111010111000001000111111010001100001001100000001010 P.jnacrophylla Pm._spergulariaeoides 110111012100000000000101121000101100001001100000001010 000000000000000000000007720000010010001001100000001010 P._polygama Pm._nuttallii 110111013100100000000101121100100101110001100000001010 000000000000000000000007720000010011000001100000000010 P._gracilis Pm.sawatchense 101111013000001000110000121101110001110001100000001010 000000000000000000000007720000000001101001100000001010 P ._ e ilia ta Pm.douglasii 001110112000001000110000101101110001110001100000001010 000000000000000000000007720100000001101001100000001010 P._basiramia Pm._australis 001110112000001000110000101101110001110001100000001010 000000000000000000000007720100000001100001100000001010 Pm._bolanderi Pm.cascadense 000000000000000000000107700001110011010100111101000100 000000000000000000000007720000010000100001100000001010 Pm._californicum Pm._engelmarmi i 000000000000000000000007700001110011010100111101000100 000000000000000000000007720100000011100001100000001010 Pm._bidwellieae Pm .jnajus 000000000000000000000007700001110011010100111101000100 000000000000000000000007720100010010001001100000001010 Pm._parryi Pm.jnontanun 000000000000000000000007700001110011110110111101010000 000000000000000000000007720177770007707001100000001010 Pm._heterosepalun Duravla 000000000000000000000007700001110101110110111101010000 000000000000000000000????7???7??????????777777????7?7? ; END; Pm._tenue BEGIN ASSUMPTIONS; 000000000000000000000007720000000011110000100001000010 OPTIONS DEFTYPE=unord PolyTcount=MINSTEPS ; Pm._shastense 000000000000000000000117721010001011011000100000000100 TYPESET * MCCURRENT = unord: 1-54; Pm._confert i florun 000000000000000000000007721001110001110001000011111001 WTSET * MCCURRENT = 1: 1-54; Pm.Jcel logi i 000000000000000000000007721001110001110001000001111001 EXSET * ALLTAXA = 11 19 24-25 30 33 35 37 50; Pm._polygaloides EXSET PGONELLA = 11 19 23-25 30 33 35 37 40-54; 000000000000000000000007721001110000110001000011101001 CHARSET PGONELLA = 1 -1 0 12-18 20-23 26-29 31 32 34 36 Pm._esotericum 38-49 51-54; 000000000000000000000007721001110001110001000011111001 Pm._paronychioides END; K> 000000000000000000000117721000011010001001100000001010 O VO Pm.jniniimm 000000000000000000000007720000000011110001000000000010 BEGIN TREES; 29 P m .a u s tra lis , 30 Pm._cascadense, [ICtadistic analyses: T) branch-and-bound (EXSET=PGONELLA) used to 31 Pm._engelmannii, establish FIG/FOG such that FOG=(fim + rob) and FIG=(Polygonella- 32 Pm._majus, FOG); 2) exhaustive search (EXSET=PGONELLA) on FIG --> s e m istric t 33 Pm._montanum, consensus tree; 3) heuristic search (closest,1 held/step; 34 Duravia TBR.HULPARS; EXSET=ALLTAXA; CONSTRAINT=PGON) done on a ll ta x a .] TRANSLATE 1 P._fimbriata. END; 2 P._robusta, 3 P._articulata, BEGIN PAUP; 4 P._parksii, CONSTRAINTS 5 P._americana, PGON=(((1,2),(3,4.C5.6), 7,8,<9,(10,11)))),12,13,14,15,16,17,18, 6 P._myriophylla, 19,20,21,22,23,24,25,26,27,28,29.30.31,32,33,34); 7 P._macrophylla, END; 8 P.jwlygama, 9 P._gracilis, 10 P._ciliata, 11 P._basiramia, 12 Pm._bolanderi, 13 Pm._cali fo rn i cum. 14 Pm._biduellieae, 15 Pm. jj a r r y i , 16 Pm._heterosepalun. 17 Pm._tenue, 18 Pm._shastense, 19 Pm._conferti fIorum. 20 P m .k e llo g ii, 21 Pm.jsolygaloides, 22 Pm._esotericum, 23 Pm.jMronychioides, 24 Pm._minimum, 25 Pm._spergulariaeoides K» 26 Pm._nuttallii, O 27 Pm._sawatchense, 28 Pm.douglasii, LIST OF REFERENCES A b r a h a m s o n , W. G. 1984a. Post-fire recovery of Florida Lake Wales Ridge vegetation. American Journal o f Botany 71: 9-21. A b r a h a m s o n , W. G. 1984b. Species responses to fire on the Florida Lake Wales Ridge. American Journal of Botany 71: 35-43. A b r a h a m s o n , W. G., J o h n s o n , A. F., L a y n e , J. N., a n d P e r o n i , P. A. 1984. Vegetation of the Archbold Biological Station, Florida: an example of the southern Lake Wales Ridge. Florida Scientist 47: 209-250. A l l e n d o r f , F. W., K n u d s e n , K . L., a n d B l a k e , G . M . 1982. Frequencies of null alleles at enzyme loci in natural populations of ponderosa and red pine. Genetics 100: 497-504. A r c h ie, J. W. 1989a. A randomization test for phylogenetic information in systematic data. Systematic Zoology 38: 239-252. A r c h ie, J. W. 1989b. Homoplasy excess ratios: new indices for m easuring levels of homoplasy in phylogenetic systematics and a critique of the consistency index. Systematic Zoology 38: 239-269. B r e m e r , K . 1990. Combinable component consensus. Cladistics 6: 369-372. B r o w n , A . H. D. 1979. Enzyme polymorphism in plant populations. Theoretical Population Biology 15: 1-42. B r o w n , A. H. D., a nd A l b r e c h t , L. 1980. Variable outcrossing and the genetic structure of predominantly self-pollinated species. Journal o f Theoretical Biology 82: 591-606. B r o w n , A . H . D ., a n d We i r , B. S. 1983. Measuring genetic variability in plant populations. Pp. 219-329 in: T a n k s l e y , S. D., a n d O r t o n , T. J. (eds.), Isozymes in plant genetics and breeding. Part A. Elsevier, Amsterdam. C a r l q u is t , S. 1962. A theory of paedomorphosis in dicotyledonous woods. Phytomorphology 12: 30-45. C a v a l l i -S f o r z a , L. L., a n d E d w a r d s , A. W. F. 1967. Phylogenetic analysis: models and estimation procedures. Evolution 21: 550-570. 211 212 C r a w f o r d , D. J. 1983. Phylogenetic and systematic inferences from electrophoretic studies. Pp. 257-287 in: T a n k s l e y , S. D., a n d O r t o n , T. J. (eds.), Isozymes in plant genetics and breeding. Part A. Elsevier, Amsterdam. C r a w f o r d , D. J. 1990. Plant molecular systematics: macromolecular approaches. John Wiley & Sons, New York. C r it c h f ie l d , W. B. 1984. Impact of the Pleistocene on the genetic structure of North American conifers. Pp. 70-118 in: L a n n e r , R. M (ed.), Proceedings of the eighth North American forest biology workshop. Logan, Utah. D a v is , M. B. 1976. Pleistocene biogeography of temperate deciduous forests. Geoscience and Man 13: 13-26. D e l c o u r t , P. A., a n d D e l c o u r t , H. R. 1981. Vegetation maps for eastern North America: 40,000 yr. B.P. to the present. Pp. 123-165 in: R o m a n s , R. C. (ed.), Geobotany II. Plenum, New York. D e l c o u r t , P. A., a n d D e l c o u r t , H. R. 1983. Late-quaternary vegetational dynamics and community stability reconsidered. Quaternary Research 19: 265-271. F a r r is , J. S. 1988. Hennig86. Version 1.5. Port Jefferson Station, New York. F e l s e n s t e in , J. 1985. Confidence limits on phylogenies: an approach using the bootstrap. Evolution 39: 783-791. F e l s e n s t e in , J. 1989. PHYLIP (Phylogeny Inference Package). Version 3.2 Manual. F l o r k in , M , a n d St o t z , E. H. (eds.) 1965. Comprehensive biochemistry. 13. Enzyme nomenclature. Elsevier Publishing Company, New York. F o w l e r , D. P., a n d M o r r is , R. W. 1977. Genetic diversity in red pine: evidence for low genic heterozygosity. Canadian Journal of Forest Research 7: 343- 347. F u e r s t , P. A., C h a k r a b o r t y , R., a n d Nei, M. 1977. Statistical studies on protein polymorphism in natural populations. I. Distribution of single locus heterozygosity. Genetics 86: 455-483. G artside , D. F., D essauer , H. C., and J oanen , T. 1977. Genetic homozygosity in an ancient reptile ( Alligator mississippiensis). Biochemical Genetics 15: 655-663. G e n t r y , A. H. 1986. Endemism in tropical versus temperate plant communities. Pp. 153-181 in: S o u l e , M. E. (ed.), Conservation biology, the science of scarcity and diversity , Sinauer Associates, Inc., Sunderland, Massachusetts. 213 G o d frey , R. K. 1978. Large-leaved jointweed. Polygonella macrophylla Small. Pp. 52-53 in: Ward , D. B. (ed.), Rare and endangered biota of Florida, Volume 5: Plants. Florida Committee on Rare and Endangered Plants and Animals, University Presses of Florida, Gainesville. G o dfrey , R. K. 1988. Trees, shrubs, and woody vines of northern Florida and adjacent Georgia and Alabama. The University of Georgia Press, Athens, Georgia. G o ttlieb , L. D. 1981. Electrophoretic evidence and plant populations. Pp. 1-46 in: R einhold , L., H arborne , J. B. and Swain , T. (eds.), Progress in phytochemistry. Vol. 7. Pergamon Press, New York. G o ttlieb , L. D. 1981. Gene number in species of Astereae that have different chromosome numbers. Proceedings of the National Academy o f Sciences USA 78: 3726-3729. G o ttlieb , L. D., and P ilz, G. 1976. Genetic sim ilarity between Gaura longiflora and its obligately outcrossing derivative G. demareei. Systematic Botany 1: 181-187. G o ttlieb , L. D., Wa rw ick , S. I., and F ord , V. S. 1985. Morphological and electrophoretic divergence between Layia discoidea and L. glandulosa. Systematic Botany 10: 484-495. H am ilton , M. J., and K ennedy , M. L. 1987. Genic variability in the raccoon Procyon lotor. American Midland Naturalist 118: 266-274. H a m r ic k , J. L. 1987. Gene flow and distribution of genetic variation in plant populations. Pp. 53-67 in: U rbanska , K . M. (ed.), Differentiation patterns in higher plants. Academic Press, New York. H am rick , J. L., and G o d t , M J. W. 1989. Allozyme diversity in plant species. Pp. 43-63 in: Brow n , A. H. D., C legg , M. T., K a hler , A. L., and Weir, B. S. (eds.), Plant population genetics, breeding and genetic resources. Sinauer Associates, Inc., Sunderland, Massachusetts. H am rick , J. L., L inhart , Y. B., a n d M itton , J. B. 1979. Relationships between life history characteristics and electrophoretically-detectable genetic variation in plants. Annual Review of Ecology and Systematics 10: 173- 200. H am rick , J. L., Mitto n , J. B., and L inhart , Y. B. 1981. Levels of genetic variation in trees: Influence of life history characteristics. Pp. 35-41 in: C onkle , M. T. (ed.), Isozymes of North American forest trees and forest insects , Pacific Southwest Forest and Range Experiment Station, Berkeley, California. H araldson , K. 1978. Anatomy and taxonomy in Polygonaceae subfam. Polygonoideae Meisn. emend. Jaretzky. Symbolae Botanicae Upsalienses 22: 1-95. 214 H e d b e r g , O. 1946. Pollen morphology in the genus Polygonum L. s. lat. and its taxonomical significance. Svensk Botanisk Tidskrift 40: 371-404. H endy , M. D., a n d D. P enny . 1982. Branch and bound algorithms to determine minimal evolutionary trees. Mathematical BioSciences 59: 277-290. H e n n ig , W. 1966. Phylogenetic systematics. Univ. of Illinois Press, Urbana. H ic k m a n , J. C. 1974. Pollination by ants: a low-energy system. Science 184: 1290-1292. H ic k m a n , J. C. 1984. Nomenclatural changes in Persicaria, Polygonum and Rumex (Polygonaceae). Madrono 31: 249-252. H ie b e r t , R. D., a n d H a m r ic k , J. L. 1983. Patterns and levels of genetic variation in Great Basin bristlecone pine, Pinus longaeva. Evolution 37: 302-310. H o l l id a y , V. T. 1990. Soils and landscape evolution of eolian plains: the Southern High Plains of Texas and New Mexico. Geomorphology 3: 489- 515. H o l s in g e r , K. £. 1990. Conservation of genetic diversity in rare plants: Principles and prospects. Abstract: ICSEB IV. Fourth International Congress of Systematic and Evolutionary Biology , University of Maryland and the Smithsonian Institution, College Park, Maryland. 1-7 July, 1990, p. 255. H o r t o n , J. H. 1960. A monograph of Delopyrum Small, Dentoceras Small, Polygonella Michx., and Thysanella Gray (Polygonaceae). Ph.D. Dissertation: University of North Carolina, Chapel Hill. H o r t o n , J. H. 1963. A taxonomic revision o f Polygonella (Polygonaceae). Brittonia 15: 177-203. H u c k , R. B„ J u d d , W. S., Wh it t e n , W. M, S k e a n , J. D., J r ., Wu n d e r l in , R. P., a n d D e l a n e y , K. R. 1989. A new Dicerandra (Labiatae) from the Lake Wales Ridge of Florida, with a cladistic analysis and discussion of endemism. Systematic Botany 14: 197-213. I m b r ie , J., a n d I m b r ie , K. P. 1979. Ice ages: solving the mystery. H arvard University Press, Cambridge, Massachusetts. J a m e s , C. W. 1961. Endemism in Florida. Brittonia 13: 225-244. J e p s o n , W. L. 1925. A manual of the flowering plants of California. Associated Students Store, Berkeley, California. J o h n s o n , A. F., a n d A b r a h a m s o n , W. G. 1982. Quercus inopina: a species to be recognized from south-central Florida. Bulletin o f the Torrey Botanical Club 109: 392-395. 215 K a r r o n , J. D. 1987. A comparison of levels of genetic polymorphism and self compatibility in geographically restricted and widespread congeners. Evolutionary Ecololgy 1: 47-58. K e p h a r t , S. R. 1990. Starch gel electrophoresis of plant isozymes: A comparative analysis of techniques. American Journal of Botany 77: 693- 712. K e s s e l i, R. V., a n d J a in , S. K. 1984. New variation and biosystematic patterns detected by allozyme and morphological comparisons in Limnanthes sect. Reflexae (Limnanthaceae). Plant Systematics and Evolution 147: 133-165. K u r z , H. 1939. Torreya west of the Apalachicola River. Proceedings o f the Florida Academy 3: 66-77. K u r z , H. 1942. Florida dunes and scrub, vegetation and geology. Florida Geological Survey, Geological Bulletin 23: 1-154. L a e s s l e , A. M . 1942. The plant communities of the Welaka area. University of Florida Press, Biological Sciences Series 4: 1-143. L a e s s l e , A. M 1958. The origin and successional relationship of sandhill vegetation and sand-pine scrub. Ecological Monographs 28: 361-387. L a g e r c r a n t z , U ., a n d R y m a n , N . 1990. Genetic structure of Norway Spruce (Picea abies): concordance of morphological and allozymic variation. Evolution 44: 38-53. L e d ig , F . T., a n d C o n k l e , M. T. 1983. Gene diversity and genetic structure in a narrow endemic, Torrey pine ( Pinus torreyana Parry ex. Carr). Evolution 37: 79-85. L e v in , D. A. 1978. Genetic variation in annual Phlox: self-compatible versus self-incompatible species. Evolution 32: 245-263. L e w is , P., a n d Wh it k u s , R. 1989. GENESTAT for microcomputers. ASPT Newsletter 2: 15-16. Li, C. C. 1976. First course in population genetics. Boxwood Press, Pacific Grove, California. L o v e , A., a n d L o v e , D. 1956. Chromosomes and taxonomy of eastern North American Polygonum. Canadian Journal of Botany 34: 501-522. L o v e , A., a n d L o v e , D. 1982. IOPB chromosome number reports LXXIV. Taxon 31: 120-126. L o v e l e s s , M. D., and H a m r ic k , J. L. 1984. Ecological determinants of genetic structure in plant populations. Annual Review of Ecology and Systematics 15: 65-95. 216 L oveless , M. D., and H am rick , J. L. 1988. Genetic organization and evolutionary history in two North American species of Cirsium. Evolution 42: 254-265. M addison , W. P., a n d M addison , D. R. 1989. Interactive analysis of phylogeny and character evolution using the computer program MacClade. Folia Primalol 53: 190-202. M axwell , J. A., and Da v is , M. B. 1972. Pollen evidence of Pleistocene and Holocene vegetation on the Allegheny Plateau, Maryland. Quaternary Research 2: 506-530. M cL eod , M J., G uttm an , S. I., E shbaugh , W. H., and R ayle , R. E. 1983. An electrophoretic study of evolution in Capsicum (Solanaceae). Evolution 37: 562-574. M endenhall , W., and Scheaffer , R. L. 1973. Mathematical statistics with applications. Duxbury Press, North Scituate, Massachusetts. M iller, R. 1950. Ecological comparisons of plant communities o f the xeric, pine type on sand ridges in central Florida. MSc. Thesis, University of Florida, Gainesville. M unz , P. A. 1973. A California flora. Univ. of California Press, Berkeley. M y e r s , R. L. 1985. Fire and the dynamic relationship between Florida sandhill and sand pine scrub vegetation. Bulletin of the Torrey Botanical Club 112: 241-252. M yers , R. L. 1990. Scrub and high pine. Pp. 150-193 in: My ers , R . L, and E w el, J. J. (eds.), Ecosystems of Florida, University of Central Florida Press, Orlando. M y e r s , R. L., and Wh ite, D. L. 1987. Landscape history and changes in sandhill vegetation in north-central and south-central Florida. Bulletin o f the Torrey Botanical Club 114: 21-32. N e i, M. 1972. Genetic distance between populations. American Naturalist 106: 283-292. N e i, M 1973. Analysis of gene diversity in subdivided populations. Proceedings of the National Academy of Science USA 70: 3321-3323. N e i, M. 1978. Estimation of average heterozygosity and genetic distance from a small number of individuals. Genetics 89: 583-590. N e i, M. 1987. Molecular evolutionary genetics. Columbia University Press, New York. N e i, M., and C h e s s e r , R. K. 1983. Estimation of fixation indices and gene diversities. Annals o f Human Genettics 47: 253-259. 217 N e i, M , and Roychoudhury, A. K . 1982. Genetic relationship and evolution of human races. Evolutionary Biology 14: 1-59. N e s o m , G. L., a n d B a t e s , V. M 1984. Reevaluation of intraspecific taxonomy in Polygonella (Polygonaceae). Brittonia 36: 37-44. O’Brien, S. J., W ildt, D. E., Goldm an, D., M errill, C. R., and Bush, M. 1983. The cheetah is depauperate in genetic variation. Science 221: 460-462. P o ja r , J. 1973. Levels of polyploidy in four vegetation types of southwestern British Columbia. Canadian Journal o f Botany 51: 621-628. SAS I n s t it u t e I n c . 1985. SAS User’s guide: Statistics, version 5 edition. SAS Institute, Cary, NC. S c h o e n , D. J. 1982a. The breeding system of Gilia achilleifolia: Variation in floral characteristics and outcrossing rate. Evolution 36: 352-360. S c h o e n , D. J. 1982b. Genetic variability and the breeding system of Gilia achillei folia. Evolution 36: 361-370. S c h w a e g e r l e , K. E., a n d S c h a a l , B. A. 1979. Genetic variability and founder effect in the pitcher plant Sarracenia purpurea L. Evolution 33: 1210-1218. Se l a n d e r , R. K., H u n g , W. G., a n d Y a n g , S. Y. 1969. Protein polymorphism and genic heterozygosity in two European subspecies of the house mouse. Evolution 23: 379-390. Sl a t k in , M. 1985. Rare alleles as indicators of gene flow. Evolution 39: 53-65. Sl a t k in , M., and B a r t o n , N. H. 1989. A comparison of three indirect methods for estimating average levels of gene flow. Evolution 43: 1349-1368. Sm a l l , J. K. 1896. Studies in the botany of the southeastern United States - VII. Bulletin of the Torrey Botanical Club 23: 407. S o l t is , D. E. 1982. Allozyme variability in Sullivantia (Saxifragaceae). Systematic Botany 7: 26-34. S o l t is , D . E ., H a u f l e r , C , H ., D a r r o w , D . C ., and G a s t o n y , G . J. 1983. Starch gel electrophoresis of ferns: A compilation of grinding buffers, gel and electrode buffers, and staining schedules. American Fern Journal 73: 9-27. Su n , M ., and G a n d e r s , F. R . 1986. Female frequencies in gynodioecious populations correlated with selfing rates in hermaphrodites. American Journal of Botany 73: 1645-1648. S u n , M., and G a n d e r s , F. R. 1988. Mixed mating systems in Hawaiian Bidens (Asteraceae). Evolution 42: 516-527. 218 Su t c l if f e , A. J. 1985. On the track o f ice age mammals. Harvard University Press, Cambridge, Massachusetts. S w o f f o r d , D. L. 1985. Phylogenetic analysis using parsimony, vers. 2.4. Computer program and documentation, Illinois Natural History Survey, Urbana. S w o f f o r d , D. L. 1990. Phylogenetic analysis using parsimony, vers. 3.0. Computer program and documentation, Illinois Natural History Survey, Urbana. Sy t s m a , K. J., a n d S c h a a l , B. A. 1985. Genetic variation, differentiation, and evolution in a species complex of tropical shrubs based on isozymic data. Evolution 39: 582-593. U n it e d S t a t e s D e p a r t m e n t o f t h e I n t e r io r . 1985. Endangered and threatened wildlife and plants; review of plant taxa for listing as endangered or threatened species. Federal Register 50 (part 17): 46. W a t r o u s , L. E., a n d Wheeler, Q. D . 1981. The out-group comparison method of character analysis. Systematic Zoology 30: 1-11. Wa t t s , W. A. 1969. A pollen diagram from Mud Lake, Marion County, north- central Florida. Geological Society o f America Bulletin 80: 631-642. Wa t t s , W. A. 1975. A late Quaternary record of vegetation from Lake Annie, south-central Florida. Geology 3: 344-346. We b b , T., III. 1981. The past 11,000 years of vegetational change in eastern North America. BioScience 31: 501-506. Weir, B. S. 1990. Genetic data analysis: methods for discrete population genetic data. Sinauer Associates, Inc., Sunderland, Massachusetts. We ir , B. S., and C o c k e r h a m , C. C. 1984. Estimating F-statistics for the analysis of population structure. Evolution 38: 1358-1370. We r t h , C. R. 1985. Implementing an isozyme laboratory at a field station. Virginia Journal o f Science 36: 53-76. Wh it n e y , M. 1896. The soils of Florida. U.S. Department o f Agriculture Bulletin 13: 14-27. Wil b u r , R. L. 1988. The authority of the binomial Polygonella gracilis. Castanea 53: 167. Wil e y , E. O. 1981. Phylogenetics: the theory and practice of phylogenetic systematics. John Wiley & Sons, New York. 439 pp. Wr ig h t , S. 1940. Breeding structure of populations in relation to speciation. American Naturalist 74: 232-248. 219 Wr ig h t , S. 1943. Isolation-by-distance. Genetics 28: 114-138. Wr ig h t , S. 1951. The genetical structure of populations. Annals of Eugenics 15: 323-354. Wu n d e r l in , R. P. 1981. Polygonella polygama (Polygonaceae) in Florida. Florida Scientist 44: 78-80. Z o n a , S. Z., a n d J u d d , W. S. 1986. Sabai etonia (Palmae): Systematics, distribution, ecology, and comparisons to other Florida scrub endemics. Sida 11: 417-427.