Great Basin Naturalist

Volume 57 Number 1 Article 1

3-7-1997

On the taxonomic status of Eriogonum robustum (Polygonaceae), a rare endemic in western Nevada

Kristin F. Kuyper University of Nevada, Reno

Ulla Yandell University of Nevada, Reno

Robert S. Nowak University of Nevada, Reno

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Recommended Citation Kuyper, Kristin F.; Yandell, Ulla; and Nowak, Robert S. (1997) "On the taxonomic status of Eriogonum robustum (Polygonaceae), a rare endemic in western Nevada," Great Basin Naturalist: Vol. 57 : No. 1 , Article 1. Available at: https://scholarsarchive.byu.edu/gbn/vol57/iss1/1

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ISSN 0017-3614

VOLUME 57 31 JANUARY 1997 No.1

Great Basin Naturalist 57(1), © 1997, pp. 1-10

ON THE TAXONOMIC STATUS OF ERIOGONUM ROBUSTUM (POLYGONACEAE), A RARE ENDEMIC IN WESTERN NEVADA

Kristin F. Kuyper1,2, Ulla Yandell3, and Robert S. Nowak1,4

ABSTRACT.~Evidence from the morphology, genetics, and biogeography of a rare endemic from western Nevada, Eriogonum mbustum, is presented to determine its most accurate taxonomic classification. Previous authors have classi­ fied E. robustum Greene both as a spedes and as a variety ofE. lobbii Torrey & Gray. However, results ofa morphometric comparison for 9 characters establish that significant morphological differentiation exists between E. robustum and E. flJbbii. In addition, results ofa genetic study using protein electrophoresis indicate that genetic differentiation may exist between these 2 taxa. Furthermore, the 2 taxa are geographically, ecologically, and reproductively isolated. :F'inally, the selective pressures that act on E. robustum in a narrowly restricted cold-desert environment are different from those that act on E. lobbii in a subalpine environment. Thus, all available data support a species-level taxonomic classification for E. robustum.

Kell words: Eriogonum robustum, Eriogonum lobbii, t/Wrpiwlogical differentiation, genetic dif.[erentiatuJn, protein electropiwrcsis, biogeugraphy, endemic species, altered mulesite soiL~.

Eriogonum Miehx. (Polygonaeeae) is a large habitats in dry climates, which results in many and widespread genus of approximately 240 geographically restricted taxa (Barneby 1989). species, Members of the genus occur mainly The large number of taxa, a complex evolu­ in western North America from northern Mex­ tionary history, and geographic isolation of ico to Alaska, although some taxa range east­ many taxa make the t.axonomy of the genus a ward to the Appalachian Mountains and penin­ puzzle that challenges those who study Erio­ sular Florida (Reveal 1989). The origin of the gonum (Howell 1975). The genus was first genus as a whole is unknown, but Reveal (1969) described by A. Michaux (1803), and early speculated it originated during the Tertiary in classifications (Bentham 1837, 1856, Torrey an arid or semiarid portion of western North and Gray 1870, Watson 1877, 1879) differed in America. Reveal further speculated tbat sub­ the number of taxonomic categories as well as genera arose at various times and in diflerent assignment of groupings by subgenera or by ge-Dgraphical areas. Some members ofthe genus sections (Myatt 1968). The taxonomy of the exhibit an ability to colonize new and unstable genus was last revised by Reveal (1969), who

IDepartrnent of Environmenta] and ResOIm;c Sei"nC(~~ /186, University ofNC"lida at Reno, Reno, NY 89557. 2prc",,,nt llddres,' Environmental Management Associates, Reno, NY 89509, 3Departmcnt ofBiology /314, University ofNevnda at Reno, Reno, NY H!l.'S57. "Author to whom reprint requests should be submitted.

1 2 GREAT BASIN NATURALIST [Volume 57

recognized 8 subgenera: Eucyc!a, Clastomyelon, Micrantha, Eriogonum, Oligogonurn, Pterogo­ num, Ganysma, and Oregonium. The taxon Eriogonum robustum Greene, "andesite buckwbeat," is one oftbe perplexing taxonomic challenges in the genus. Eriogonum robustum is a narrowly restricted endemic that NEV~D~ occurs on "islands" of hydrothermally altered andesite in the vicinity ofReno, Nevada (Fig, 1), The classification of E. robustum in the litera­ ture is riddled with inconsistency (Table 1): Eriogonum robustum has been classified both nOOAADQ as a species and as a variety of E. lobbii, The * species E. lobbii was first described by Torrey * and Gray (1870), and their description of its range included the area that populations of E, robustum currently occupy, However, in 1885, Greene recognized E. robustum as a very local species. He also recognized similarities be­ tween E. robustum and E, lobbii and placed the new species "between E. compositum and E. lobbii," However, Jones (1903) reclassified E, robustum as E. lobbii var, robustum, In her Fig. 1. Locations of Eriogunum robustum populations revision of the genus, Stokes (1936) agreed (boxes) and the nearest populations of E. lubbii (stars) in with Jones; because E. robustum is more robust west central Nevada and east central California (locations than E, lobbii, she stated that E. robustum "is from the Nevada Natural Heritage Program 1994 database doubtfully even a variety, for superior nourish­ and personal observations). ment would account for the differences.·" However, Billings (1950, 1992) considered E, robustum a "good species" and refelTed to it as of species differentiation is based solely on such, He pointed out that the substrate on morphological distinctness; i.e., a species is a which E. robustum is naturally fouud (i.e" group of organisms that are more similar mor­ islands of altered andesite) is low in nutrients, phologically to other individuals within the and thus "superior nourishment" could not group than they are to any other group, The account for the large size of E. robustum. The biological species concept is based on repro­ classification of E. robustum as a variety or as a species is not the only inconsistency: the ductive isolation behiveen groups oforganisms. spelling of the variety epithet also varies. For According to this concept, a species is a group example, MullZ (1968) referred to the plant as ofindividuals or natural populations that inter­ E, lobbii var, robustius; Reveal (1985a) used breed but are reproductively isolated from other another spelling, E. robustium. The correct groups. Under the selection concept, a species orthography is robustum. For convenience, we is a system of genetically similar individuals, reference E. robustum as a distinct species in Genetic identity is maintained as a cohesive this paper, unit by a set of selective pressures that balance The purpose of this study was to assess the the disruptive forces imposed by environmental taxonomic classification of Eriogonum robus­ factors, mutation, and genetic recombination. tum by investigating the extent to which it and Finally, the evolutionary species concept defines E, lobbii differ, The criteria for determining species as a spatio-temporallineage ofpopula­ whether or not 2 taxa are separate species tions that evolve separately from other lineages depend on the species concept applied. Species and occupy their own ecological niche. In this concepts generally fall into 4 categories (510­ paper we utilize information from a compre­ bodchikoff 1976): typological, biological, sclec­ hensive literature review, data from our mor­ tive, and evolutionary. The typological concept phological measurements and from a limited 1997] TAXONOMIC STATUS OF ERIOGONUM ROBUSTUM 3

TABLE 1. Chronology ofreferences to Eriogonum mbustum in the literature.

Date Author Taxonomy 1870 Torrey, J., and A. Gray Eriogonum lohbii 1885 Greene, E. L. Eriogonum rohustum 1903 Jones, M. E. Eriogonum lohhii val'. robustum 1925 Tidestrom, I. Eriogonum rohustum 1936 Stokes, S. Eriogonum lohbii val'. mbustllm 1950 Billings, W. D. Eriogonum robustum 1968 Munz, P. A. Eriogunum lobbii val'. robu.sUus 1975 Howell, J. T. Eriogonum robustum 1980 Mozingo, H., and M. Williams Eriogonum lobbii var. rolnwtum 1985a Reveal, J. L. Eriogonum robustium 1985b Revoal, J. L. Eriogonum lohhii val'. robustum 1987 Km"tez, J. T. Eriogonum lobbii val'. robustum 1989 Reveal, J. L. Eriogonum lohbii val'. mbustum. 1992 Billings, W D. Eriogonum robustum 1992 Northern Nevada Native Plant Society Eriogonum lobbii vaT. rohustum 1992 Morefield, J., and T. Knight (eds.) El"iogonum robustum

electrophoretic study, and observations over 4 simple versus compound. The quantitative growing seasons to assess the most appropriate characters were petiole length, lamina length, taxonomic classification of E. robusturn with­ lamina width, involucre length, flowering stem in the framework of these different species length, flowering stem width, bract length, and concepts. bract width. These characters were chosen because ofreported differences for those traits MATERIALS AND METHODS and the feasibility of measuring them from herbarium specimens. Petiole length was mea­ Morphological Analyses sured from the point of its attachment on the Eighty-three dried herbarium specimens of caudex to the base ofthe lamina. Lamina length Eriogonurn robusturn and 383 specimens ofE. was measured from the base to the tip. Lam­ lobbii were examined. The specimens were ina width was measured at the widest point of located at the University of Nevada, Reno, the leaf. Involucre length was the distance herbarium (RENO) or loaned by 1 of the fol­ from the point of its aItachment on the ray to lowing herbaria: Bailey Hortorium (BH includ­ the tip of the middle lobe. Flowering stem ing CU), Natural History Museum (BM), length was measured from its point of attach­ Brigham Young University (BYU), California ment on the caudex to the first series ofbracts State University, Chico (CHSC), University of subtending the umbel. Flowering stem width the Pacific (CPH), University of California, was measured 4 cm below the bracts. Bract Davis (DAV), Field Museum of Natural His­ length was measured from the point of aItach­ tory (F), Harvard University Herbaria (GH), ment on the flowering stem to the tip of the University of Idaho (ID), University of Cali­ bract. Bract width was measured at the widest fornia, Berkeley (JEPS), Missouri Botanical point of the bract. For the quantitative charac­ Garden (MO), Nevada State Museum (NSM), ters, 3 replicate measurements of each charac­ California Polytechnic State University (OBI), ter were made on every plant specimen. These USDA Forest Service, Region 4, Ogden replicate measurements were then averaged (OGDF), Pacific Union College (PUA), Rancho to derive the sample measurement for each Santa Ana Botanic Garden (RSA), Santa Bar­ individual herbarium specimen. bara Botanic Garden (SBBG), San Jose State A rankit plot and the Wilt-Shapiro statistic University (SJSU), Smithsonian Institution were use to examine normality of the data for (US), Universily of California, Berkeley (UC), each of the 8 quantitative characteristics. The University of Nevada, Las Vegas (UNLV), and rankit plots were nearly linear and the approx­ Utah State University (UTC). imate Wilt-Shapiro statistics were between 0.90 One qualitative and 8 quantitative charac­ and 0.99, indicating that the data did not devi­ ter traits were chosen for morphological analy­ ate greatly from normality. Because sample ses. The qualitative trait was umbel structure: variances were often not equal among sample 4 GREAT BASIN NATURALIST [Volume 57

populations, nonpammetric statistics were used continuous tris-citrate buffer system (gel bufi"r: to compare means. A lann-Whitney (2-sample 0.003 M citric acid, 0.015 ,I tris; electrode rank sum) test was conducted for each quanti­ buffer: 0.1 M sodium hydroxide, 0.3 M boric tative character to determine if a mean value acid; Schuster et al. 1989) utilizing horizontal for Eriogonum lobbi; was significantly differ­ gel electrophoresis. The histidine II buffer sys­ ent from that for E. mbustum. A Kruskal-Wallis tem (buffer # 18) of King and Dancik (1983) one-way analysis of variance with mean com­ resolved hexoseaminase (E.C. 3.2.1.52) at pH parison was used to compare the 3 sample 7.0 and resolved at least 1 distinguishable locus populations: E. lobbii with simple umbels, E. of malate dehydrogenase (E.G. 1.1.1.37), pos­ lobbii with compound umbels, and E. mbustllm sibly 2, at pH 8.0. Although these methods (which uniformly had compound umbels). In were repeated for fresh leaf material collected addition, a principal components analysis (PCA) in 1994, no distinct banding patterns occurred was performed on the 8 quantitative variables during electrophoresis and we were not able to order the specimens in multidimensional to resolve any loci. space. Pearson's correlations were computed lor all 8 quantitative characteristics and the REsu!:..s AND DISCUSSION PCA values from axes 1 and 2; tests of signifi­ Morphological Differentiation cance for the correlation coefficients followed procedures given in Sokal and Rohlf (1981). For plants growing in their natural habitat, STATlSTX Version 4.1 (Analytical Software, Eriogonum robustum ha... features that distin­ Tallahassee, FL) was used for the nonparamet­ guish it from E. lobbi; and all other buck­ ric tests and Pearson's correlations, and PC­ wheats (Billings 1950 and personal communi­ ORO Version 2.0 (MjM Software Design, cation, Morefield personal communication, Gleneden Beach, OR) was used for the PCA Mozingo and Williams 1980). E,iogonum lob­ aonlysis. bi; is a small, low-spreading form, whereas E. robustum is a larger, more robust form, as its Protein Electrophoresis name implies. Published descriptions of the Protein electrophoresis was used to deter· plants differ in growth form, leaf characters mine the extent ofgenetic divergence between (size and pubescence), and floral form (in£lo­ Eriogonum lobbii aDd E. robustum using E. rescence habit, umbel structure, and color; caespitosu-m as an outgroup. Fresh, young leaf Table 2). material wa, collected in July and August 1993. Significant differences existed between Eri­ Leaves were then ground in liquid nitrogen ogonum robust",,, and E. lobbii for all 8 quan­ and the samples mixed with the grinding buffer titative cbaracters that we measured (Table 3). of Bayer and 1inish (1993). We were able to For all characters except flowering stem length, resolve 7--8 putative loci, most of them (phos­ E. robustum had a larger mean than E. lobbi; phoglucose isomerase, E.G. 5.3.1.9; gluconate (Fig. 2). The differences in character size be­ dehydrogenase, E.C. 1.4.1.2; diaphorase, E.C. tween E. robustllm and E. lobbii were large for 1.8.1.4; superoxide dismutase, E.C. 1.15.1.1) flowering stem width and bract width, where on a modified version of the Poulik (1957) dis- the means for E. robustum were, respectively,

TAULE 2. Morphological comparison ofEriogonutn robuS'turn and E. lohhii (Mozingo and \iVilliams 1980, Kartez 1987, 13arneby 1989, Reveal 1989, Hickman 1993). Character Eriogonum lohbii Eriogonum robustum Growth form Seldom hranched near hase Much branch~d near base H~ight: 0.3--1.5 dm Height.: 1.0--3.0 dm Width: 0.5-4.0 dm Width: 1.0-3.5 dm Tomentose on lower surface Tomentose entirely Length: 1.0-5.0 em Length: 2.5--5.0 em Peduncle Decumbent, hranched ncar tip Erect, mostly unbranched Length: 6-20 em Length:]8 em Umbel.> Simple, sometimes compound Compound Ray #: 2-6 Ray #, 15 Flow~r (,'Olor: cream to yellow aging red Flower color: eream to yellow 1997] TAXONOMIC STATUS OF ER1OGONUM ROBUSTUM 5

TABLE 3. P values from Mann-Whitney tests and from Kruskal-Wallis one-way analyses of variance for 8 quantilative characters measured on Eriogorwm lobbii and E. robustum herbarium specimens. FOT the Kruskal-Walhs analyses, signifi- cant differences between means for a particular character are indicated by different letters; units for all means are mm.

Petiole Lamina Lamina InvoLucre Flowering Flowering Bract Bract Compa.'ison length length width length stem length stem 'width length width

All E. lobbii V$. E. robustum <0.001 <0.001 <0.001 <0.001 0.036 <0.001 <0.001 <0.001 (Mann-Whitney) E. lobbii with simple umbels V$. E. lobbii with compound <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 umbels V$. E. rohustum (Kruskal-Wallis AOV) K·W mean comparisons: E. lobbii, simple umbels 16.6a 21.9a 15.5a 7.7a 89.5a l.Oa 1O.8a 2.80 E. lohbii, compound umbels 22.2b 29.0b 21.2b 8.9b IOS.5b 1.3b 14.9b 4.3b E. robwtum 21.7b 31.9b 21.2b 9.lb 82.5a 2.00 17.7c 4.90

100% aDd 60% greater than those for E. lobbii., set of E. lobbii with compound umbels com­ but small for flowering stem length and in­ pared with tbose of the more typical E. {obbii volucre length, wbere the means for E. robus­ and with those of E. robustum. Significant dif­ tum were 10% smaller and 15% greater than ferences existed between the smaller subset of tbose for E. lobbii. Ranges in cbaracter size E. lobbii and E. robustum for 4 ofthe 8 charac­ overlapped for all characters, but the extent of ters measured. The 2 subsets of E. lobbii dif­ overlap for 95th percentiles was small for fered significantly for all 8 characters (Table 3). flowering stem width and for bract length. In summary, results of the morphological The 2 taxa formed nearly distinct clusters comparison of the 2 taxa show that a signifi­ when plotted in the 2-dimensional space of cant amount of morphological differentiation ..xis 1 and axis 2 from the PCA of the 8 quanti­ exists between Eriogonum robustum and E. tative characters (Fig. 3). Eriogonum robustum lobbii. Significant differences between tbe 2 occurred primarily on the left side ofaxis 1 and taxa occurred in all 8 quantitative as well as in on the lower part of axis 2. Eriogonum lobbii the 1 qualitative character measured. Principal occurred primarily on the upper part ofaxis 2, components analysis separated the samples with the subset of E. lobbii with compound into nearly discrete groups that corresponded umbels primarily on the left side of axis 1 and with taxonomy, Despite significant differences the subset of E. lobbii with simple umbels on iu morphological characteristics, construction the right side of axis 1. PCA axis 1 accounted of a dichotomous key to separate the 2 taxa is for 71% of the total variance and axis 2 for difficult, especially a key to use on herbarium 11%. Lamina length, bract length, and lamina specimens. Clearly, ifthe specimen has simple width were most highly correlated with axis 1 umbels, then it is E. lobbii. However, speci­ (Table 4). Flowering stem length, flowering stem mens with compound umbels can be either width, and petiole length were the 3 charac­ taxon; for these specimens, flowering stem ters most highly correlated with axis 2. All cor­ length and flowering stem width appear to be relations were significant with the exceptions the best characteristics to differentiate the taxa. of lamina length, lamina width, and involucre Both characters were significantly different length with respect to ..xis 2 (Table 4). between E. lobbii with compound umbels and The frequency of simple and compound E. robustum, and they were most highly corre­ umbels differed between taxa (Table 5). One lated with PCA ..xis 2, which was the PCA axis hundred percent of E,iogonum robustum had that separated this E. lobbii subset from E. compound umbels, whereas only 16% of E. robustum. The mean flowering stem length for lobbii did. Segregation of the character was herbarium specimens of E. lobbii with com­ significant between Iaxa as detennined by a pound umbels was 105 mm (95% CI of 98­ chi-square test. A one-way analysis of variance 113), and that ofE. ,·obustum was 83 mm (95% was performed to detennine bow the quantita­ CI of77-88); mean flowering stem width ofE. tive morphological characteristics of the sub- lobbii with compound umbels was 1.3 mm (95% 6 GREAT BASIN NATURALIST [Volume 57

60 15 + an inflorescence, shorter petioles and smaller + .<: .<: 50 + ~ leaves are diagnostic of E. lobbii: petiole ~ + 12 0> 0> $ c: c: 40 - length of 16-18 mm, lamina length of 21-23 - 9 mm, and lamina width of 15-16 mm corre­ " 30 "~ $$ 6 0 spond with the 95% CI for the subset of E. "0 20 m .. f--L "0 lobbii with simple umbels. Unfortunately, speci­ n. 3 > 10 -'- c: mens with petiole length > 19 mm, lamina ,, , , 0 0 length >30 mm, and lamina width >20 mm .<: 50 could be either taxa, as the 95% CIs for these ~ + 32 .<: * ~ 0> c: 40 * * -c characters overlap for E. robustum and for the * 24 ';1: " 30 T T subset of E. lobbii with compound umbels. In '"c: $ $ 16 '"c: the field other characters such as flowering E 20 • • E ..L stem growth habit (prostrate or erect), relative ..J'" 10 8 ..J'" , density of tomentum on the lamina, and num­ .<: ,,, ~ 0 0 .<: 0> $ ~ ber ofrays are also useful. c: 160 + ) " + 3 Reproductive Isolation E 120 T * E 2 The distributions of the 2 taxa do not over­ 0> 80 • 0> *c: *$ *c: lap (Fig. 1). Eriogonum lobbii occurs on grav­ .<: .<: 40 -'- $ ~+ 1 elly, rocky, or clayey slopes and ridges from ~ "~ ,, , , approximately 1800 to 3650 m in the northern U- 0 0 U- Coast Ranges of California north to southern + + 30 8 Oregon and in the Sierra Nevada of California .<: + .<: 0, 24 i and western Nevada (Reveal 1989). The distri­ c: i * 6 -c- J1 18 ';1: bution of E. robustum is restricted to altered 15 4 15 !!! 12 $E§ !!! andesitic soils in the Reno region, ranging from III III 6 2 1310 to 2440 m in elevation (Billings unpub­ , lished). As of 1994 there were 15 confirmed 0 0 .' .' populations of E. robustum (Nevada Natural Heritage Program personal communication), located in the VIrginia Range, on Peavine Moun­ tain, and in Sun Valley north of Reno. Spatial and ecological barriers between populations of Fig. 2. Box plots for 8 quantitative morphological char­ acters of 383 Eriogonum lobbii and 83 E. robustum her­ E. robustum and E. lobbii likely formed during barium specimens; units for all measurements are mm. the climatic changes since the late Pleistocene Filled diamonds represent mean values; horizontal lines (Billings 1950, DeLucia and Schlesinger 1990). near the center of the boxes indicate the median; lower Not only are Eriogonum robustum and E. and upper edges of the box represent the 25th and 75th geographically isolated, but the nearest percentiles; error bars below and above the box indicate lobbii the 5th and 95th percentiles; the points indicated by a + interspecific populations are separated by dis­ represent possible outliers. tances that are large relative to the expected dispersal potential ofboth taxa. In addition, the taxa are largely seasonally isolated due to the CI of 1.2-1.4), and that of E. robustum was 2.0 elevation differences in their ranges. Eriogonum mm (95% CI of 1.9-2.1). For specimens with­ robustum flowers in March through August; out a clear umbel structure, flowering stem E. lobbii flowers in July through September length is a less reliable character (Fig. 2), and (NNNPS 1992). the larger bract size should be coupled with Geographical, seasonal, and ecological isola­ larger flowering stem width to identifY E. tion prevent genetic exchange, which can even­ robustum. The 95% CIs for bract length and tually lead to reproductive isolation and the width are 17-19 mm and 4.6-5.2 mm, respec­ formation of distinct evolutionary units. Other tively, for E. robustum versus 10-11 mm and examples of this pattern in genera with relict 2.7-3.0 mm for E. lobbii with simple umbels populations in Nevada can be found in Pole­ and 14-16 mm and 3.8-4.7 mm for E. lobbii monium (Grant 1989) and Ipomopsis (Grant and with compound umbels. For specimens without Wilken 1988). Another result of geographical, 1997] TAXONOMIC STATUS OF EIUOCONUM ROBVSTUM 7

0.2 ,------,======;] o E. Iobbil, simple umbels • E. Iobbii, compound umbels o ~ E. robus/um, compound umbels

0.1

0.0

-0.1

-0.2 ':-__-':-__--L-__--:-__---'-__----:'---_-----.J -3 -2 -1 0 1 2 3 PCAAxis 1

Fig. 3. Principal component analysis of 8 quantitative morphological characters measured from herbarium specimens of Eriogonum lobbii and E. robu.stum. Inset: mean and standard deviation of axis 1 and axis 2 values for E. [obbii with simple umbels (open circles), E. lobbii with compound umbels (filled circles), and E. f"obu.stum (filled triangles). seasonal, and ecological isolation can be mor­ We attempted to replicate and expand the phological differentiation. electrophoretic survey in 1994 but were unable to resolve the same enzyme systems that year: Genetic Differentiation Because the late winter and spring of1994 were A tantalizing pattern appeared in the 1993 much drier than the corresponding periods in electrophoretic trials. An unidentified isozyme, 1993, we suspect that the plants had modilled diagnostic to species, appeared on system 26 their physiology enougb to alter the electro­ for the following enzyme stains: aspartate amino­ phoretic results. possibly by changing the ratio transferase (E.C. 2.6.1.1), phosphoglucose iso­ of the amounts of active enzymatic proteins to merase, and gluconate dehydrogenase. The secondary compounds, which in turn inhibits bands of the unidentified isozyme moved far­ electrophoretic resolution. We had also con­ thest in Eriogonum robusturn samples, 0.9 as ducted electrophoretic trials with different far for E. lobbii, and were absent for E. caespi­ buffers for leaves collected in October 1992, tosunc A pattern of this sort suggests a possi­ but none ofthese trials were successful. ble genetic marker differentiating all 3 taxa. Evolutionary Divergence However, sample sizes were very small (4 E. lobbii, 5 E. caespitosum, and 10 E. robusturn Eriogonum robustum and E. lobbi.i are both individuals) with only 1 population ofeach taxa placed in the subgenus Oligogonum Nutl. sampled. Thus, although it is an unlikelyoccur­ (Reveal 1969). Oligogonum includes 32 species rence, we cannot absolutely rule out the possi­ in 7 sections that are widely distributed through­ bility that these markers are population-spe­ out most ofwestern North America with 1 dis­ cific rather than species-specific. junct species in the Appalachian Mountains. 8 GREAT BASIN NATURALIST [Volume 57

TABLE 4. Pearson's correlation coeHlcients between each TABLE 5. Number of' herbarium specimens with simple of the 8 morphological characters and scores from axis 1

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