Introgression in Purshia Tridentata (Pursh) DC. and Cowania Stansburiana Torr

Brigham Young University BYU ScholarsArchive

Theses and Dissertations

1957-01-01

Introgression in Purshia tridentata (Pursh) DC. and Cowania Stansburiana Torr

Lindsey Kay Thomas Brigham Young University - Provo

Follow this and additional works at: https://scholarsarchive.byu.edu/etd

BYU ScholarsArchive Citation Thomas, Lindsey Kay, "Introgression in Purshia tridentata (Pursh) DC. and Cowania Stansburiana Torr" (1957). Theses and Dissertations. 7991. https://scholarsarchive.byu.edu/etd/7991

This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. INTROGRESSIONIN PURSHIATRIDENTATA (PURSH) DC. ANDCO\VANIA STANSBURIANA TORR.

LINDSEYKAY THOMAS, JR.

A THESIS PRESENTED TO 1'HE FACULTY OF THE DEPARTMENT

OF BOTANYIN PARTIALFULFILLMENT OF THE REQUIREMENTS

FOR THE DEGREEOF MASTEROF SCIENCE

BRIGHAMYOUNG UNIVERSITY

1957

HARO\.D S. LEc U8P/\PY BRIGHAM YOUNG u;,1:vrns1r. PROVO.UTAH

ACKNOWLEDGMENTS

Special thanks are extended to Dr. Howard c. Stutz ot the Brigham Young University for suggesting the problem, aid in collecting most of the populations studied, and for his advice on methods of research and the writing of this paper.

The author gratefully acknowledges the help received from Dr. c. Lynn Hayward of the Brigham Young University for his advice, and the help received from Dr . G. Ledyard Stebbins , Jr. of the Universie ty of California for his loan of the plant . material f-rom California. Thanks are extended to Keith Shaw and Richard Nelson for their aid in collecting some of the populations .

The patience of my wife, Nancy, during the researeh and writing of this paper, as well as her help in collecting some of the plants, is gratefully acknowledged.

ii CONTENTS

Page

ACKNOWLEDGMENTS.• • • • • • • • • • • • • • • • • • • • • • ii INTRODUCTION• • • • • • • • • • • • • • • • • • • • • • • • 1 METHODS. • • • • • • • • • • • • • • • • ...... • • • • 2 RESULTS. • • • • • • • • • • • • • • • • • • • • • • • • • • 11

DISCUSSION • • • • • • • • • • • • • • • • • • • • • • • • • 54 Population Dynamics •••••••••••••••• • •. 55 Origin of Pur$hia gl!ndulosa ••••••••••••••• 59 Location ot Parental Types• •••••••••••••• • 60 Evolution in Purshif trident1ta • • ••••• • • •• • • 62

C.ONCUJSIONS • • • • • • • • • • • • • • • • • • • • • • • • • 64 • • • • • • • • • • • • • • • • • • • • • • • • • 65 ABSTRACT • • • • • • • • • • • • • • • • • • • • • • • • • • 67

iii INTRODUC'rION

Introgress i on of one species into another often occurs in the zone of distributional overlap of the species , and is recognized by the presence of discordant variat i on (Anderson , 1951) . This dis - cordant variation was recognized in a population of eliffroses (Cowani a Stansburiana. Torr . ) growing at Edgemont , Utah (near Provo) .

The discordant variation was suspected to have been introduced from bitterbrush (Purshia tridentata (Pursh) DC. ) . The following report is of a study which was undertaken to determine whether intro gres - sion was taking place in this and other populations of Cowania

Stansburiana and also in selected populations of Purshia tridentata .

An examination of two populations of Purshia glandulosa Curran (Mojave Antelope Bush) left on loan by Dr. G. Ledyard Stebbins , Jr . of the University of California indicated that this species might be a stabilized hybrid segregant of Purshia tridentata and Cowania Stanaburiana , since the set of characters that characterize this species seems to be a combination of characters that belongs to the Purshia tridentata and Cowania Stansburiana complexes . A study was undertaken to determine whether there was any real basis for this indication . This study of introgression is si milar to other intro gression studies that have been made within the past few years and employs the methods and techniques outlined by Anderson (1949) .

l METHODS

The first step in the study of intro gression was to become thoroughly acquainted with the morphology that characterized each of the three species: Purshia tridentata , Purshia glanduloea, and

Cowania Stansburiana . This was done by carefully studying the plant material and comparing it with the taxonomic descriptions of Abrams

(1940) and Rydberg (1913) . After a study of the distribution of Purshia tridentata and C9wania Stansburiana via these taxonomic works , it was decided to concentrate on the plants from California because there was less possibility of their being in the range of distributional overlap with each other and therefore they would have a greater possibility of being pure species .

Information gained from the above study enabled variation to be recognized in the field . In obtaining the population samples one twig was taken from each plant; the plants were picked at ran- dom, and in the case of those collected by the author , the plants were collected along a line transect. An attempt was made in collecting the samples to obtain twigs with fruits and hypanthia.

Each population sample consisted of from eleven to twenty-three twigs . When examining the twigs for pubescence , the twig nearest the observer as it was removed from the newsprint where it had been pressed was selected . The topmost undamaged flower was selected tor the flower studies. An inspection of the leaves in each whorl

2 3 of several whorls of each species indicated that they were similar enough that the largest leaf could be taken to represent the whorl; this leaf is also more easily worked with than the smaller leaves.

The third whorl from the top of the branch in the intras pe cies studies and the tenth whorl from the top of the braneh in the intrapopulation studies was selected unless it was obvious th at the largest leaf was missing or the leaves were immature; in these cases the next whorl down in which the largest leaf was present was se• lected. Stud ies ot the intraplant, intraspeeies, and intrapopulation variation were made on the material collected by using the following characters. For those characters used in the hybrid index and s catter diagrams the grades are also given . l. Young twig pubescen ce. The relative density was noted and scored in three grades: O for very heavy pubescence . 1 for intermediate, and 2 for none. 2. Number of leaf lobes. Distinct notches in the leaves were counted as separate lobes in the intraplant and intras pec ies studies. In t he intrapopulation studies this was scored in six grades for the hybr id indices and in nine grades for the scatter diagrams as follows: 0 for three definite lobes, 1 for three definite lobes and a tendency (notch or tooth) for more lobes, 2 for four definite lobes , 3 for four definite lobes with a tendency for more , ill• On the hybrid index a score of five re pres ents not only a tendency for more than five lobes, but also more than five lobes, while on the scatter diagrams a score of five represents only a tendency for moro than five lobes. 4

3 . Leaf length-width ratio . This was measured in millimeters at the greatest length and greatest width.

4 . Leaf lobe length - width ratio. This was measured in milli - meters on the lowest lobe . The width was measured at the junction ot the lobe with the rest of the leaf and at right angles to the ax - is of the lobe. The length was measured from the tip to the point where the width measurement was taken.

5 . Leaf pubescence density . The relative density on the top , bottom , or both sides of the leaves was noted . The pubescence on the upper surface of the leaves was scored in three grades in the intrapopulation studies.

6 . Leaf-margin revolution . This was either noted as being heavily or slightly revoluted or was measured in tenths of a millimeter to obtain the ratio of the outside measurement of the apex lobe to the distance between the revoluted margins of the same lobe .

The measurements were taken at the junction of the apex lobe with the r~st of the leaf . This was scored in two grades .

7. Upper leaf surface glandulosity. The number of large punctate glands within one square millimeter were counted on the lowest lobe as near to the apex as could be acconunodated by the grid . This was scored in three grades: 0 for no glands , 1 for one or two glands per square millimeter . and 2 for three or more glands per square millimeter. The glands on the margin ot the leaf were included in the measurement even though some of the glands were on the bottom side of the leaf; these glands were generally apparent from the top of the leaf . 8 . Hypanthium length-width ratio. This was measured at the 5

grea t est length and greatest width in millimeters .

9 . Hypanthium glandulos i ty . The gr i d was cent ered over the side of each hypanthium and the number of glands within one square millimeter was counted. This was scored in three grades: 0 for no

glands • 1 for one or two glands per square millimeter , and 2 for

three or 1nore glands per square millimeter .

10 . Hypanthiwn pubescence. This was noted as being either present or absent . This was scored in two grades .

11 . Stalkedneas of hypanthium glands . The degree of stalked - ness was noted and scored in three grades: 0 when the glands were

appressed to the hypanthium or were la cking , 1 when the glands were nubs , and 2 when the glands were stalked .

12 . Petal color. This noted qualitatively . 13 . Number of stamen series . The number of series was count -

ed and scored in two grades .

14 . Stamen insertion . This was noted and s cored in two

grades! 0 for insertion on the margin of the hypanthium , 1 for in •

se rt ion in the throat of the hypanthium .

15 . Pistil number . The number was counted and scored in

three grades: 0 for one or two pistils , 1 for three pistils• and 2

for four or more pistils .

16 . Mature achene shape . This was determined by computing

the length - width ratio in millimeters at the greatest length and

greatest width of the achene . The scoring was in three grades: 0

tor a ratio of 3. 1 or less , 1 for a ratio of 3 . 2 , and 2 for a ratio

of 3 . 3 or more.

17 . Style length in fruit . This was measured in centimeters 6 from the tip to the point of attachment with the achene and was scored in three grades ·: 0 for one and a half centimeters or less ,

1 for the intermediate measurements , and 2 tor three and a half cen • timeters or more . 18 . Style pubescence . This was noted and scored in three grades . All observations of these characters were made under a nine - power Spen c er dissecting microscope equipped with a linear and grid ocular micrometer and a stage grid (square millimeters) . For all the characters that were measured quantitatively except number of stamen s~ries and pistil number the mode, mean , range , and standard deviation were calculated . Since some of the characters used in the study of intraplant and intraspecies variation (leaf length - width ratio , leaf lobe length - width ratio , hypanth i um length-width ratio • petal color) were found to be nondiagnostic , they were not used in constructing the hybrid indices or scatter diagrams which were used in the analyses of the intrapopulation variation . By using the scored characters , as noted above, the hybrid indices were constructed in a manner such that 1!• tridentata was given the low score and£ • Stansburiana was given the high score . A summary of the grades and scores of the hybrid index is shown in the table below (Table 1) .

Since many of the plants in some of the populations lacked some of their parts , all of the characters used in one hybrid index could not be used in another hybrid index. However . all the charac - ters that were used in the hybrid index of any one population were also used in the construction of the scatter diagram of that popula - 7

TABLE 1 SUMMARY OF THE GRADESAND SCORES USEDIN COMPUTINGTHE HYBRIDI NDEX

Character f• tridentata Intermediate £· Stansburiana

Twig pubescence 0 1 2

Leaf lobes , 0 or l 2 or 3 4 or 5 number

Leaf margin , 0 • • • • • 1 revolution

Leaf surface, 0 1 2 glandulosity

Leaf surface, 0 1 2 pubescence

Hypantbium 0 1 2 glandulosity

llypanthium 0 1 2 glands, stalkedness

Hypanthium 0 • • • • • 1 pubescence

Pistil number 0 1 2

Style length 0 1 2 in fruit

S.tyle pubescence 0 . 1 2

~tamen series , 0 • • • • • 1 number

Stamen insertion 0 • • • • • 1 Mature achene , 0 1 2 length-width ratio

tion . Since the number of leaf lobes and the glandulosity of the upper leaf surface could be measured fairly exactly in a series of 8 grades , they were used as the co-ordinates in all the scatter diagrams . The other ch aracters were represented on the diagram by shading different parts of the dot and adding whiskers of different lengths at certain places on the periphery of the dot as described by Anderson (1949). The key to the scatter diagrams is shown below

(Table 2).

The scatter diagrams were useful in determining which characters tend to segregate together. The characters that were in the minority were extrapolated to have come from one parental population type, while the characters that were found in the majority of the members of the population were extrapolated to have come from another parental population type. Extrapolation to the putative parental population types was made for each of the populations .

Eight populations were analyzed using all fourteen of the di- agnostic characters: Toiyabe Purshia tridentata population (from boundary of Toiyabe National Forest , California); White Mountain ,

California!: • glandulosa population #2; Kanosh , Utah£ • Stansburiana population ; Cove Fort , Utah mixed population of!:• tridentata and £• Stansburiana; Dividend , Utah mixed population; Oak City, Utah mixed population; Motoqua, Utah Purshia glandulosa population; and

Dubois, Idaho!'.. • tridentata population. A population of!'..• tridentata from Pocatello, Idaho and a pop - ulation off• tridentata from Uelena , Montana were each analyzed by using the same fourteen characters except young twig pubescence . The followin g populations were analyzed by using all the diag- nostic characters except mature achene shape, style length in fruit , and style pubescence: White Mountain• California£• glandulosa pop - 9 TABLE 2

KEY TO FIGURES 2 TUROUGH19

Number of Leaf' Lobes 3 3+a 4 4+ 5 5+ 6 6+ 7 ' 7+

Score 0 1 2 3 4 5 6 7 8 9

Pubescence of Young Pubescence of Upper Hypanthium Twigs Surface of Leaves Glandulosity

0 fairly pubescent 0 fairly pubescent 0 no glands

1 or 2 glands/ 6 in termediate 0 intermediate 0- sq. mm.

glabrous glabrous 0- 3 or more glands/ b d sq . mm.

Stalkedness of the Pistil Number Style Length Hypanthium Glands in Fruit glands appressed 0 to surfa.-;e or 0 1 or 2 pistils 0 1. 5 cm. or less lacking

Q nubs Q 3 pistils p 1.6 to 3 . 4 cm. O....stalked 9 4 or more pistils ? 3 . 5 cm. or more Ratio of Length/ Width Style Pubescence Leaf Margin n of Mature Achene Revolutio

0 puberulent 0 3. 1 or less 0 sli ght

-0 intermediate b 3 . 2 (! heavy

-0 plum ose b 3 . 3 or more . • •

Hypanthium Number of Stamen Pubescence Series Stamen Insertion

0 present 0 one 0 hypanthium margin <. glabrous " more than one hypanthiwn throat aThe symbol n+nindicates a tendency for more lobes. 10 ulation #1; Polson, Montana?• tridentata population; Malad, Idaho f• tridentata population; Escalante, Utah Cowania Stansburiana population; and Kanab, Utah£• Stansburiana popul ation.

A population of£• Stansburiana from F..dgemont, Utah was scored by using the same fourteen characters except young twig pubescence, mature achene shape, and style length in fruit.

In the analysis of a population of£• Stansburiana from Scipio Pass, Utah and a mixed population from Pine Valley, Utah the following five characters were used: young twig pubescence, number of leaf lobes, leaf-margin revolution, upper leaf surface glandulosity, and pubescence on the upper surface of the leaves. RESULTS

From a study o!' the distribution of tile three species as outlined by Abrams (1940), Rydberg (1913), and others (Benson, 1951; McMinn. 1951; Kearney , 19424 Peek , 1941; Preston, 1940; Forest Berv~ ice, 1937; Wooton, 1915) with respect to political divisions, physi • ographic features, and vegetative zones or types and from a study of vegetation maps prepar~d by Lynch (1924) for Canada and Shantz

(1923) for the United States , an attempt was made to construct a map which would demonstrate the distribution of the three species under study and their zones of overlap with each othor. This is shown below in Figure 1.

From a detailed analysis of plant specimens and from a study . 0£ taxonomic descriptions furnished by Rydberg (1913) and Abrams

(1940) the distinctive characteristics of each species were formu• lated. These a.re swnmarized below in Table 3.

After a general knowledge of the characteristics of each species had been obtained (Table 3), the variation of some of the characters within a single f • tridentata and a single£• Stansbur!ana plant were studied. The distributional map (Fig. 1) indicates that f • tridentata from northern California and£• Stansburiana from southern California would best represent nonintrogressed samples. As shown in the table (Table 4) there is considerable intraplant variation, particularly in Cowania Stansburiana .

11 12

U6" 110· 100·

i i ; L.' __ _ r ,,--~ :----,--+.-,- ·-·-·------··,---i __, ~- i I i I ·-1•-·---L It--- .. KY 7 ------_J ___ Purshia tridentata -~ ~ / -- --+- ,, - - -,- - 7 O i I I Purshia glandul� O I I -f ___ _ --,·-'-- Cowania Stasburiana O / ,~----, i I I I I I i i I .I r-- ____J ·-·1

25 ------~-

m·

Fig. 1. • Distribution map of Prshia tridentata, Purshia glandulosa, and Cowania Stansburiaa in western North Aerica. 13

'f ABLE 3

A COMPARISON OF THE CHARACTERISTICS OF THE PLANTS COWANIA STANSBURI ANA, PURSHIAGLANDULOSA, AND PURSHIA TRIDENTATA Characters -c. Stansburiana f· glandulosa f· tridentata Young twig no pubescence no pubescence pubescent pubescence

Leaf shape obovate cuneate cuneate

pinnately 3 5 or more cleft; - 3•cleft at apex, Leaf margin it 3 divid ed , · 3-cleft (rarely sometimes the the divisions $-cleft) at apex .Sivisions a gain again divided .-iotched or ' toothe d or toothed

Leaf-margin strongly rev- strongly rev- weakly rev- revolution oluted margin oluted margin oluted margin

glandul a r- punctate on Leaf glandu- glandular- margins and no punctate losity . punctate above some on lower glands and upper surface Pubescence glabrous or of upper sli ghtly pubescent above leaf glabrous above pubescent surface above

few glandu- Hypanthium glands only a lar hairs glandu- stalked glands slightly when glands losity stalked are present

Hypanthiwn essentially tomentulose tomentulose pubescence none

Pistil 4 12 1 or l or 2 number - 2 oblong, Seed shape linear oblong , obovate obovate

Style length 3.9 5.8 cm. 1.5 cm." long 1.5 em. lon g in fruit long - or less or less 14

TABLE3 - Continued Characters -c. Stansburiana f• glandulos'?- f• tridentata distinctly Pubescence puberulent, not puberulent, not of style plumose, llairs measurable measurable 1-1.5 mm. long

Stigma terminal dec ur rent on de current on position one side one side Number of stamen series 2 series l series 1 series

Stamen inserted in inserted on inserted on insertion throat of margin of margin ot hypanthium hypanthiwa hypanthium

lanceolate. fusiform, or fusiform, or Achene shape or oblong obovate obovate Pubescence villous-hirsute short velvety of achene (on upper end) pubescent pubescent

Achene none very slightly very slightly glandulosity glandular glandular

TABLE4

A COMPARISONOF INTRAPLANTVARIATION IN COWANIASTANSIJUR~ANA ANDPUR.sHIA TRIDENTATA

Item Nb -X R M s Number or leaf lobes c. Stansburiana 40 s.o 3 .. 7 s.o 0.79 -P . tridentata 20 3.1 3 .. 4 3.0 0.30 Length ...width of leaf in mm. £• Stansburiana 40 1.4 1.1--2.3 1.3 0.32 .E• ti-identata 20 2.4 1.a-2.9 2.5 0.35 Length-width leaf lobe in mm. £· Stansburiana 40 1.7 0.5 ...3.0 2.0 o.s1 E.• t:ridentata 20 1.4 o.s ...3.0 1.3 0.51 Leaf-mar gin revolution in mm. £· Stansbu~iana 40 2.2 1.5-3.3 1.s o.46 -P. tride.ntata 20 1.3 1.1-1.e 1.4 o.14 15 TABLE4 - Continued

Item N -X R M s Glands/sq. mm. on top of leaf c. St .~nsburiana 40 5.6 3-10 7.0 1.77 i. tridentata 20 o.o 0 o.o o.oo Hypanthium length-width in mm. c. Stansburiana 24 1.6 1.0-2.0 1.4 0.28 - 1.s 2.0 P. tridentata 15 1.6 o.a.. 3.2 1.0 o.74 - 1.2 1.6 1.7 Glands/sq. mm. on hypanthium c. Stansburiana 24 5.1 3-9 a.o 1.26 -!!• tridentata 15 o.o 0 o.o o.oo Mature achene length-width in mm. c. Stamtburiana 18 4.5 3.2-a.s 4.0 o.94 -P. trident .a ta 20 2.0 1.5-3.2 1.s o.45 Length ot style in cm. c. Stansburiana 20 s.o 3 •.9-5.8 s.a 0.61 i>. tridentata 20 0.4 0.2-0.55 0.40 0.10 0.45 - o.so

Item N Upper Side Lower Side

Pubescence of leaves c. Stan§buriana 40 sparse, or heavy - glabrous !!• tridentata 20 moderate heavy Item N Color Petal color c. Stan$bttriana 10 yellow .!!•- tridentata 10 yellow

b N = total number measured; - X = meani R = range; M = mode; S = standard deviation.

In order to discover the difference betw~en intraplant varia• t:lon and intraspecies variation, several plants each of!::• triden- 16

!.!!,! and£• Stansburi ana were studied by using the same characters as were used in the intraplant vari at ion study except that hypanthium pubescence was studied instead of upper leaf surface glandulosity. The!!• trident ata plants th at were examined were from Cali- fornia (Toiyabe population), but since there was only one specimen of£• Stansbur!ana available from California, plants from the Kanab,

Utah population were used. Although Kanab is within the distribu• tional range of!!• tridentata, a thorough analysis of a population sample revealed no signs of introgression (see Fig. 16). The intraspecies variation (fable 5) shows£• Stansburiana to be quite variable when compared to£• tridentata. As is shown by a comparison of Tables 4 and 5, the variation within a species is quite similar to variation within a single plant of the species.

TABLE5 A COMPARISONOF INTRASPECIESVARIATION IN PURSHIATRIDENTATA ANDCOWANIA STANSBURIANA

Item N -X R M s Number ot leaf lobes c. Stansburiana 20 s.o 3•7 s.o o.s2 -f· tridentata 20 3.0 3 3.0 o.oo Length-width of leaf in mm. £• Stansbur iana 12 1.6 1.2-2.1 1.6 0 .. 26 1.8 .f• tridentata 12 2.1 1.6-2.8 2 .. 2 o.33 Length-width of leaf lobe in mm. £· Stansburiana 10 2.0 . 1.5-3 .. 0 2.0 0.37 .t• trigentata 10 1.5 1.0-2.0 1.0 0.44 2.0

Glands/sq. mm. on hypanthium c. Stansbur iana 10 6.? 5•8 7.0 ·o.95 -f• tridentata 10 o.o 0 o.o o.oo 17 TABLE 5 - Continued

Item N -X R M s Hypanthium length~width in mm. f• Stansburiana 10 1.5 o.s-2.a 0 ,.8 o.63 1.2 1.7 !!• tridentata 10 1.0 o.s-1.1 o.9 0.10 1.0

Mature achene length•width in nun. £•. Stansburiana • • ••• ·-· - -· f•. tridentata 10 2.1 1.7-2.7...... 2.0·-··· 0.30. . Length of style in cm. c. Stansburiana • • .. .. • ••••••• • ••• • ••• f. triden;!:ata 10 0.4 0.25-0.6 0.30 0.35 0.35 0.40 o.so

Item N Upper Side Lower Side Pubescence of leaves Stansb\lriana 10 sparse ., or heavy £· glabrous E• trid.entata 10 moderate heavy Item N Degree of Revolution

Leaf-margin revolution at apex c. Stansburiana 10 strong revolution £·- tridentata 10 slight revolution Item N Pegree of Pubescence

Hypanthium pubescence £· Stansburiana 10 none E· tridentata 10 slightly pubescent Item N Color Petal color £• Stansburiana 10 yellow -P. tridentata 10 yellow

From the results of the foregoing investigations (Tables 3,

4, and 5) the most constant and most characteristic morphologies 18 were selected in constructing the hybrid indices and the pictori- alized scatter diagrams. The hybrid index scores for each of the eighteen populations analyzed are found in Tables 6 thr~ugh 23, and the scatter diagrams for the same populat ions are found in Figures

2 through 19. As shown in the scatter diagrams the extrapolates were in the direction of£~ Stansburiana , Purshia tridentata, or .f• glandulosa.

TABLE6 HYBRIDINDEX SCORESIN THE TOIYABEPOPULATION

Plant Number Score P . tridentata • • • • • • • • • • • • • • • • • • • • 0 or 1 Stanshuriana • • • • 26 or 27 -1c. • • . • • • • • • • • • • • • • " • • • • • • • • • • • . • . • • • • • • • 0 2 • • • • • • • • • • • • • • • • • • • • • • • • • 0 3 .. • . • • . • . • • • • • . • • • • • . • • • • 3 4 • • • • • • • • • • • • • • • • • • • • • • • • • 0 5 • • • • • • • • • • • • • • • • • • • • • • • • • 0 6 • • • • • • • • • • • • • • • • • • • • • • • • • 1 7 • • • • • • • • • • • • • • • • • • • • • • • • • 0 8 • • • • • • • • • • • • • • • • • • • • • • • • • 0 9 • • • • • • • • • • • • • • • • • • • • • • • • • 0 10 • • • • • • • • • • • • • • • • • • • • • • • • • 0 11 • • • • • • • • • • • • • • • • • • • • • • • • • 0 12 • • • • • • • • • • • • • • • • • • • • • • • • • 1 13 • • • • • • • • • • • • • • • • • • • • • • • • • 0 14 • • • • • • • • • • • • • • • • • • • • • • • • • 0 15 • • • • • • • • • • • • • • • • • • • • • • • • • 0 16 . . . . - ...... • • • 0 17 • • • • • • • • • • • • • • • • • • • • • • • • • 0 18 • • • • • • • • • • • • • • • • • • • • • • • • • 0 19 • • • • • • • • • • • • • • • • • • • • • • • • 0 20 • • • • • • • • • • • • • • • • • • • • • • • • • 0 21 • • • • • • • • • • • • • • • • • • • • • • • • • 0 22 • • • • • • • • • • • • • • • • • • • • • • • • • 0 19

(1)

c:U rw 7 Sot =l'IJ as ""'C> .... 6 Sot (1) §c c.,. 5 0 a• a'• 4 . fl.I Sot (1) P. f1l "1::1 3 e:cs ....t.,

1 .,...... '

0 1 2 J 4 5 f 6 7 8 9 Score of lobes per lea£ Fig. 2 . - Scatter diagram for the characters scor ed for the Toiyabe population . 20

TABLE 7 HYBRID INDEXSCORES IN TUE WHITE MOUNTAIN POPULATION #2

Pl a nt Number ~co re P. t r i dent at a •• • • • • • • • • • • • • • • • • • • 0 or 1 -c. St ansb ur i ana . • • • • • • • • • • • • • • • • • 26 or 27 -1 • • • • • • • • • • • • • • • • • • • • • • • • 9 2 • • • • • • • • • • • • • • • • • • • • • 12 3 • • • • • • • • • • • • • • • • • • • • • • • 8 4 • • • • • • • • • • • • • • • • • • • • • • • 14 5 • • • • • • • • • • • • • • • • • • • • 12 6 • • • • • • • • • • • • • • • • • • • • • • 12 7 • • • • • • • • • • • • • • • • • • • • • • • 11 8 • • • • • • • • • • • " • • • • • 8 9 • • • • • • • • • • • • • • • • 11 10 • • • • • • • • • • • • • • • • 10 11 • • • • • • • • • • • • • • • • • 9 12 • • • • • • • • • • • • • • • • • 10 13 • • • • • • • • • • • • • • • • • • • • • 7 14 • • • • • • • • • • • • • • • • • • • • • • 10 15 • • • • • • • • • • • • • • • • 8 16 • • • • • • • • • • • • • • • • • • • • • • • 13 17 • • • • • • • • • • • • • • • • • • • • • • • 12 18 • • • • • • • • • • • • • • • • • • 11 19 • • • • • • • • • • • • • • • 14 20 • • • • • • • • • • • • • • • • • 11 21 • • • • • • • • • • • • • • • • • • • • • • • 18 22 • • • • • • • • • • • • • • • • • • • • • • • • 14 23 • • • • • • • • • • • • • • • • • • • • • • 13 21

10 2,-- ~------...... - ..... 9 ' ...... ~--\'~~,.. ----~~~>f- -...... 0~ 8 " " ' \ cs 7 \ " ' I M ""::I l Ill ft.I «I 4) 6 I ,-j I Sot I p. I := I 5 ~& I ""0 I • I I I ¥~ ( { 0"• 4 © c(- I .J? I 4) I "'1-'l. / tC i4 _.,,,/ 'ti 3 -

0 l 2 3 4 5 6 7 8 9 Score of lobes per leaf Fig . 3. - Scatter diagram for the characters scored for the White Mountain population #2 . 22

TABLE 8

HYBRIDINDEX SCORES IN THE KANOSH POPULATION

Plant Number Score ...P. tridentata • • • • • • • • • • • • • • • • • • • • 0 or 1 c. Stansburiana • • • • • • • • • • • • • • • • • • • 26 or 27 -1 • • • • • • • • • • • • • • • • • • • • • • • • • 22 2 • • • • • • • • • • • • • • • • • • • • • • • • • 25 3 • • • • • • • • • • • • • • • • • • • • • • • • • 26 4 • • • • • • • • • • . • • • • • • • • • • • • • • 22 5 • • • • • • • • • • • • • • • • • • • • • • • • • 22 6 • • • • • • • • • • • • • • • .. • • • • • • • • • 25 7 • • • • • • • • • • • • • • • • • • • • • • • • • 25 8 • • • • • • • • • • • • • • • • • • • • • • • • • 24 9 • • • • • • • • • • • • • • • • • • • • • • • • • 25 10 • • • • • • • • • • • • • • • • . • • • • • • • • 26 11 • • • • • • • • . • • • • • • • • • • • • • • • • 26 12 • • • • • • • • • • • • • • • • • • • • • • • • • 23 13 • • • • • • • • • • • • • • • • • • • • • • • • • 24 14 • • • • • • • • • • • • • • • • • • • • • • • • • 23 15 • • • • • • • • • • • • • • • • • • • • • • • • • 20 16 • • • • • • • • • • • • • • • • • • • • • • • • • 22 23

t I \ \ \ I \ I \ I 'I .o I ~I o I -}1

*'~I I I' I I I I ,,.I ,,,. ; .. \ \ ( I I I I I I ,,1 I I ,- / ,,I' / ,,,/ Exf;-ca.pof<.,.fi:Y;,,, ,,. ,, 0 '.- ----..------_,_. - - - - - , --

• 3 4 5 6 7 t 8 9 Score or' lobes per leaf ' ' Fig . 4. - S~atter diagram for the characters scored for the Kanosh population. 24

'fABLE 9 HYBRIDINDEX SCORES IN THE COVEFORT POPULATION

Pl an t Number Sc or e P . t r i dent 2;ta • • • • • • • • • • • • • • • • • • • • 0 or 1 St ansl>u r iana . • • • • • 26 or 27 c.-1 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 2 • • • • • • • • • • • • • • • • • • • • • • • • • 12 3 • • • • • • • • • • • • • • • • • • • • • • • • • 15 4 • • • • • • • • • • • • • • • • • • • • • • • • 6 5 • • • • • • • • • • • • • • • • • • • • • • • • • 0 6 ••••• • •••• • • • • • • • • . . .' •· . . • • 9 7 • • • • • • • • • • • •- • • • • • •• • • • • • 8 8 ...... •· • • • • • • • • ...... • • 10 9 • • • • • • • • • •- . • • • • • • • • • • • • • 4 10 ••• • •••••• • • • • • • • • .,..... • • 10 11 • • • • •• • • • • • • • • • • • • • • • • • • • • 6 12 • • • • • • • • • • • • • • • • . .' •· . •· . • • 5 13 • • • • • • •• • • ·- . • • • • • • • • • • • • • • 5 14 ...... • • • • • • • • • ••••• • • • 2 15 • • • • • • • • • • • • • • • • ... •· .. • • 24 16 ... •· ..... • • • • • • • • • • • • • • • • 24 17 • • • • • • • • • • • • • • • • • • • • • • • • • 26 18 • • • • • • • • • • • • • • • • ...... • • 2 19 • • • • •• • • •• • • • • • • • • • • • • • • • • • 25 20 • • • • • • • • • • • • • • • • • • • • • • • • • 25 21 • • • • • • • • • • • • • • • • • • • • • • • • • 25 22 • • • • • • • • • • • • • • 5 25

8 *

* I I I I I /

I o~•..., I ...... _ 3 I I ( / '- .....

2 \ \ \ \

O t 1 t 2 • 3 t 4 ' 5 1 6 7 8 9 Score of lobes per leaf Fig .. 5. - Scatter diagram for the eharacters scored tor the Cove Fort population . 26

TABLE 10 HYBRIDINDEX SCORESIN THE DIVIDENDPOPULATION

Plant Number Score £• tridentata • • • • • • • • • • • • • • • • ti • 0 or 1 f.• Stansburia9:4 . • • • • • • • • • • • • • • 26 or 27 1 • • • • • • • • • • • • • • • • • • • • • • • • • 24 2 • • • • • • • • • • • • • • • • • • • • • • • • • 6 3 • • • • • • • • • • • • • • • • • • • • • • • • 6 4 • • • • • • • • • • • • • • • • • • • • • • • • 0 5 • • • • • • • • • • • • • • • • • • • • • • • • • 5 6 • • • • • • • • • • • • • • • • • • • • • • • • • 8 7 • • • • • • • • • • • • • • • • • • • • • • • • • 24 8 • • • • • • • • • • • • • • • • • • • • • • • • 23 9 • • • • • • • • • • • • • • • • • • • • • • • • 3 10 • • • • • • • • • • • • • • • • • • • • • • • • 25 11 • • • • • • • • • • • • • • • • • • • • • • 16 12 • • • • • • • • • • • • • • • • • • • • • • • • • 7 13 • • • • • • • • • • • • • • • • • • • • • • • • 4 14 • • • • • • • • • • • • • • • • • • • • • • 13 15 • • • • • • • • • • • • • • • • • • • • • • • • • 18 16 • • • • • • • • • • • • • • • • • • • • • • • • • 5 17 • • • • • • • • • • • • • • • • • • • • • • • • • 5 18 • • • • • • • • .. • • • • • • • • • • • • • • • • 8 19 • • • • • • • • • • • • • • • .. • • • • • • • • • 4 20 • • • • • • • • • • • • • • • • • • • • • • • • • 0 21 • • • • • • • • • • • • • • • • • • • • • • • • • 4 22 • • • • • • • • • • • • • • • • • • • • • • • 8 23 • • • • • • • • • • • • • • • • • • • • • • • • • 4 27

£-id,-a._p.I-. f/o,, 8 (, ,/;------·- ...... ------. ....

Q> g 7 ' \ ' \ I. afl) I cU 6 I ....ct> I k I o; ,::i,. go 5 I 0 I • I ' I I • 4 / ti' / fO / k 4> ,:ll, fl.) 3 "O *~ t:,.... ' \ 2 l I I I I l I 1 I l I I

2 3 4 5 6 7 8 9 Score of lobes per leaf Fig . 6 . - Scatter di agram fo r the characters s c ored tor the Divi dend popu l ation . 28

TABLE 11

HYBRID INDEX SCOllliS IN THE OAK CITY POPULATI ON

Plan t Number Score E.• tr i dentata •• • • • • • • • • • • • • • • • 0 or 1 £• Stansbur i ana . • • • • • • • • • • • • • • • • • • 26 or 27 l • • • • • • • • • • • • • • • • • • • • • • • • • 26 2 • • • • • • • • • • • • • • • • • • • • • • • • 2 3 • • • • • • • • • • • • • • • • • • • • • • • • • 1 4 • • • • • • • • • • • • • • • • • • • • • • • • • 0 5 • • • • • • • • • • • • • • • • • • • • • • • • 4 6 - ...... • • • • • • • • • • • • • • • • • • 3 7 • • • • • • • • • • • • • • • • • • • • • • • • • 2 8 • • • • • • • • • • • • • • • • • • • • • • • • • 0 9 • • • • • • • • • • • • • • • • • • • • • • • • • 5 10 • • • • • • • • • • • • • • • • • • • • • • • • • 0 11 • • • • • • • • • • • • • • • • • • • • • • • • • 1 12 • • • • • • • • • • • • • • • • • • • • • • • • • 3 13 • • • • • • • • • • • • • • • • • • • • • • • • • 26 14 • • • • • • • • • • • • • • • • • • • • • • • • • 25 15 • • • • • • • • • • • • • • • • • • • • • • • • • 27 16 • • • • • • • • • • • • • • • • • • • • • • • • • 2 17 • • • • • • • • • • • • • • • • • • • • • • • • • 7 18 • • • • • • • • • • • • • • • • • • • • • • • 27 19 • • • • • • • • • • • • • • • • • • • • • • • • • 26 20 • • • • • • • • • • • • • • • • • • • • • • • • • 1 21 • • • • • • • • • • • • • • • • • • • • • • • • • 6 29

41 ·(> 7 ....ell ' tO '\ ft-I \ : 6 l ·"'4 I I ... l 4) * I' §' 5 I (t,f 0 ( ( ( **** I

2 *

d 0 2 3 4 5 6 7 8 9 Score of lobes per leaf

Fig. 7. Scatter diagram for the characters scored for the Oak City population. 30

TABLE 12 HYBRID INDEXSCORES I N THE MOTOQUAPOPULATION Plant Number Seore f • t rident ata . • • • • • • • • • • • • • • • • • 0 or 1 f • Stansburiana . • • • • • • • • • • • • • • • • • • 26 or 27 1 • • • • • • • • • • • • • • • • • • • • • • • 15 2 • • • • • • • • • • • • • • • • • • • • • • • • • 13 3 • • • • • • • • • • • • • • • • • • • • • • • • • 14 4 • • • • • • • • • • • • • • • • • • • • • • • • • 13 5 • • • • • • • • • • • • • • • • • • • • • • • • • 17 6 • • • • • • • • • • • • • • • • • • • • • • • • • 10 7 • • • • • • • • • • • • • • • • • • • • • • • • • 9 8 • • • • • • • • • • • • • • • • • • • • • • • • • 16 9 • • • • • • • • • • • • • • • • • • • • • • • • • 13 10 • • • • • • • • • • • • • • • • • • • • • • • • • 14 11 • • • • • • • • • • • • • • • • • • • • • • • • • 12 12 • • • • • • • • • • • • • • • • • • • • • • • • • 14 13 • • • • • • • • • • • • • • • • • • • • • • • • 11 14 • • • • • • • • • • • • • • • • • • • • • • • • • 12 15 • • • • • • • • • • • • • • • • • • • • • • • • • 14 16 • • • • • • • • • • • • • • • • • • • • • • • • • 10 17 • • • • • • • • • • • • • • • • • • • • • • • • • 10 18 • • • • • • • • • • • • • • • • • • • • • • • • • 13 19 • • • • • • • • • • • • • • • • • • • • • • • • • 11 20 • • • • • • • • • • • • • • • • • • • • • • • • 13 2 1 • • • • • • • • • • • • • • • • • • • • • • • • • 13 22 • • • • • • • • • • • • • • • • • • • • • • • • • 9 23 • • • • • • • • • • • • • • • • • • • • • • • • • 11 31

10 {) .+ I I

9 I 'I

I I 8 I

l I

I I I I I I' I

I ._.,,,yJ,-_ ..~d,,_J&J,,..--- , \ \ I I l I I 3 I I I I I I I 2 I / ,/

/ / 1ot'l. / / Ex t t-'f;.I'~I .!'- +.....- 4 - - -

0 l 2 3 4 5 6 7 8 9 Score of lobes per leaf

Fig . 8 . - Scatter diagram for the characters scored for the Motoqua population . 32

TABLE 13 HYBRIDINDEX SCORES IN THE DUBOISPOPULATION

Pl an t Number Score f.• tr i dentata . • • • • • • • • • • • • • • • • • • • 0 or 1 c. St ansburiana • • • • 26 or 27 - 1 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 6 2 • • • • • • • • • • • • • • • • • • • • • • • • • 4 3 • • • • • • • • • • • • • • • • • • • • • • • 5 4 • • • • • • • • • • • • • • • • • • • • • • • • • 6 5 • • • • • • • • • • • • • • • • • • • • • • • • 4 6 • • • • • • • • • • • • • • • • • • • • • • • • • 3 '1 • • • • • • • • • • • • • • • • • • • • • • • 6 8 • • • • • • • • • • • • • • • • • • • • • • • 6 9 • • • • • • • • • • • • • • • • • • • • • • • • • 4 10 • • • • • • • • • • • • • • • • • • • • • • • • • 5 11 • • • • • • • • • • • • • • • • • • • • • • 4 12 • • • • • • • • • • • • • • • • • • • • • • • • • 3 13 • • • • • • • • • • • • • • • • • • • • • • • • • 4 14 • • • • • • • • • • • • • • • • • • • • • • • • • 6 15 • • • • • • • • • • • • • • • • • • • • • • • • • 8 16 • • • • • • • .. • • • • • • • • • • • • • • • • • 5 17 • • • • • • • • • • • • • • • • • • • • • • • • • 5 18 • • • • • • • • • • • • • • • • • • • • • • • • • 5 19 • • • • • • • • • • • • • • • • • • • • • • • 4 20 • • • • • • • • • • • • • • • • • • • • • • • • • 4 33

Cl> 0 7 (;$ ...;.. ::s QI fH IU 6 .... "4 Cl) t:l, §4 5 ft-I 0 • I 4 0'• Ill J.t (I> t:l, a} 'ti ....fd t, 1 21

0 1 2 3 4 5 6 7 8 9 Score of lobes per leaf

Fig . 9. - Scatter diagram for the characters scored for the Dubois population . 34

TABLE 14 HYBRIDINDEX SCORES IN THE POCATELLOPOPULATION

Plant Number Score P. tridentata • • • • • • • • • • • • • • • • • • • • 0 or 1 £· StansJ?uriana. • • • • • • • • • • • • • • • • • • 24 or 25 1 ...... • • • • • • • • • • • • • • • • • • 6 2 • • • • • • • • • • • • • • • • • • • • • • • • 2 3 • • • • • • • • • • • • • • • • • • • • • • • • • 3 4 • • • • • • • • • • • • • • • • • • • • • • • • • 2 5 • • • • • • • • • • • • • • • • • • • • • • • 7 6 • • • • • • • • • • • • • • • • • • • • • • • • • 4 7 • • • • • • • • • • • • • • • • • • • • • • • • • 0 8 . . , . . . . • • • • • • • • • • • • • • • • • • 1 9 • • • • • • • • • • • • • • • • • • • • • • • 5 10 , ...... • • • • • • • • • • • • • • • • • • 1 11 ...... • • • • • • • • • • • • • • • • • • 4 12 ...... • • • • .. • • • • • • • • • • • • • 0 13 • » • • • • • • • • • • • • • • • • • • • • • 0 14 • • a • ·• • • • • • • • • • ii • • • • • • • • • • 0 15 ...... • • • • • • • • • • • • • • • • • • 2 16 ...... • • • • • • • • • • • • • • • • • • l 17 • • • • • • • • • • • • • • • • .. • • • • • • • • 3 18 ...... • • • • • • • • • • • • • • • • • 3 19 • • • • • • • • • • • • • • • • • • • • • • • • • 0 20 • a • • • • • • • " • • • • • • • • • • • • • • 2 21 • • • • • • • • • • • • • • • • • • • • • • • • • 4 35 10

8 . Cl> u 7 I'll Sol ""'::, (IJ CM CIS 6 ...Cl) r.. Cl) i:i. §' 5 ft-4 0 • Ii 4 C"• r.o r.. Cl> i:i. 3 i::: ....t'II " 2

0 1 2 4 5 6 7 8 9 Score of lobes per leaf

Fig. 10. - Scatter diagram for the characters scored for the Pocatello population. 36

TABLE 15 HYBRIDINDEX SCORESIN THE HELENAPOPULATION

Plant Number Score P. tridentata • • • • • • • • • • • • • • • • • • • 0 or 1 c. Stansburiana. • 24 or 25 -1 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 7 2 • • • • • • • • • • • • • • • • • • • • • • • • • 8 3 • • • • • • • • • • • • • • • • • • • • • • • • 9 4 • • • • • • • • • • • • • • • • • • • • • • • • • 8 5 • • • • • • • • • • • • • • • • • • • • • • • • • 6 6 • • • • • • • • • • • • • • • • • • • • • • • • 4 7 • • • • • • • • • • • • • • • • • • • • • • • • • 6 8 • • • • • • • • • • • • • • • • • • • • • • • • • 7 9 • • • • • • • • • • • • • • • • • • • • • • • • • 9 10 • • • • • • • • • • • • • • • • • • • • • • • • • 8 11 • • • • • • • • • • • • • • • • • • • • • • ••• 7 12 ' • • • • • • • • • • • • • • • • • • • • • • • • • 7 13 • • • • • • • • • • • • • • • • • • • • • • • • • 9 14 • • • • • • • • • • • • • • • • • • • • • • • • • 5 15 • • • • • • • • • • • • • • • • • • • • • • • • • 6 - 16 • • • • • • • • • • • • • • • • • • • • • • • • • 5 17 • • • • • • • • • • • • • • • • • • • • • • • • • 6 18 • • • • • • • • • • • • • • • • • • • • • • • • • 8 19 • • • • • • • • • • • • • • • • • • • • • • • • • 9 20 • • • • • • • • • • • • • • • • • • • • • • • • • 8 21 • • • • • • • • • • • • • • • • • • • • • • • • • 6 22 • • • • • • • • • • • • • • • • • • • • • • • • • 8 37

¢1 7 u i,s t:, ,...fl.! (U 6 ....QI S.. QI :,8: 5

0 • m • 4 04 Cll S.. QI

{D 3 (\- 'ti cl- c{- t..-o.P.ol...+,. 11 ~1-.. ------a _, ' 0 / 'I """ __,. I 2 -e..

1 c(

0 3 4 5 6 8 9 Score of lobes per leaf

Figv 11~ - Scatter diagram tor the characters scored for the Helena population. 38

TABLE 16 HYBRIDINDEX SCORES IN THE WHITE MOUNTAIN POPULATION #1 Plant Number Score .f• tridentatn •• • • • • • • • • • • • • .. • • 0 or 1 f.• Stansburiana. • • • • • • • • • • • • • • • • • 20 or 21 1 • • • • • • • • • • • • • • • • • • • • • • • • • 8 2 • • • j • • • • • • • • • • • • • • • • • • • • 10 3 • • • • • • w • • • • • • • • • • • • • • • • 8 4 • • • • • • • • • • • • • • • • • • • • • • • • • 9 5 . . . - . . • • • • • • • • • • • • • • • • 8 6 • • • • • • • • • • • • • • • • • • • .. • • • • • 8 7 w • • • • • • • • • • • • • • • • • • • • • • • • 9 8 • 4 • • • • • .. .. • • • • • " • • • • 8 9 ...... • • • • • • • • • • ol " • • • 10 10 • • • • • • • .. • • • • • • • 7 11 . . . . . • • • • • • • • • • • • • • • • • 7 12 • • • • w • • .. • • • • • • • • • • • • .. • 8 13 • • • • • • • • • • • • " • • • • • • • • • • • 6 14 • • • • • • • • • • • • • • • • • • " • • • • 8 15 • • • • • • • .. • • • • • • • • • • • • • • • • • 9 16 • • • • • • • • • • • • • • • • • • • • • • • • • 10 17 • • • • • • • • • • • • • • • • • • • • • • • 10 18 • • • • • • • • • • • • • • • • • • • • ' " • • 9 19 • • • • • • • • • • • • • • • • • • • • • • • • • 11 20 • • • • • • • • • • • • • • • .. • • • • • • • 10 21 • • • • • • • • • • • • • • • • • • • • • • • • • 9 22 • • • • • • • • • • • • • • • • • • • • • • • • • 8 23 • • • • • • • • • • • • • • • • • • • • • • • • • 7 39

II) 0 7 'M '1"' ::s ell -... «I 6 C) ,-j s.. C) ,:lo §4 5

1 2 3 4 5 6 7 8 9 Score of lobes per leaf

Fig~ 12~ Scatter diagram for the characters scored f or the White Mountain population #1. 40

TABLE17

HYBRIDINDEX SCORES IN THE POLSONPOPULATION Plant Number ,. Score f• tridentl'lta • • • • ; " • .. • • $ • • • • • • • • 0 or 1 c. S4;ansbll!"iana • 20 or 21 -1 • • • • • • • • • • • • • • • • • • • .J ...... • • • .. ·• • . • • • • • • • 5 2 • •. • • • • • • • • • • • • • • • • • • • • • • • 4 3 • • • • .) • • • • ·• • • .. • • • • • • • • • .. • • 4 4 • • 0 • • • • • .. .. • .. • • • • • • • • .. • • • .. 5 5 I) • • • • .. • • • • • . .. • • • • • • • • . • • • 7 0 ,, ., 6 • • • .. • " • • .. .. • • • • • • • • .. • • • 6 7 • • • • • • .. • • • • ... .. • .. .. • .. • • • • • 4 8 • • • • 0 0 • • .. " • •- " • .. • • • .. • • • • • • 6 9 0 0 $ 6 • • • • • • .. • • • • • • • " • • • • • • • 0 ,, 0 ., 10 • .. • • 0 ,, • • • • • • • • • • • • • • • 6 11 .. 0 • • • • • 0 • • • • 0 0 • • • • • • • • • .. 6 12 0 0 0 0 " 5 • • • • • " • • • • • • .. • • • • • • .. 13 0 0 0 0 ,0 (I ;i 0 ,I 5 • .. " • • " • . .. • . • .. .. . • 14 0 0 ,, 0 0 IJ,I 4 .. .. • • • .. • " • • • • • • • . • • .. 41

(') 0 7 1\1 (_,. f.c ::s t6 fM <11 6 ....IP

G) ""0. ll. ::, 5 ft-4. 0. § 4 • O' (lj

0."" Ill 3 "'a ....c.,

0 l 2 i ' 4 5 6 7 8 9 Score of lobes per leaf' '

Fig. 13. Scatter diag~am for the characters scored for the Polson population. 42

TABLE 18

HYBRID INDEXSCORES IN THE MALADPOPULATION

Plant Number Score P. tridenta:t~ • • • • • • • • • • • • • • • • • • • • 0 or l c. Stansburiana • • • • • • • • • • • • • • • • • • 20 or 21 -1 • • • • • • • • • • • • .. • • • • • • • • • • • • 4 2 • • • • • • • • • • • • • • • • • • • • • • • • • 6 3 • • • • • • • • • • • • • • • • • • • • • • • • • 1 4 • • • • • • • • • • • • • • • • • • • • • • • • • 3 5 • • • • • • • • • • • • • • • • • • • • • • • • • ., 6 • • • • • • • • • • • • • • • • • • • • • • • • • l 7 • • • • • • • • • • • • • • • • • • • • • • • • • 2 8 • • • • • • • • • • • • • • • • • • • • • • • • • 5 9 • • • • • • • • • • • • • • • • • • • • • • • • • 0 10 • • • • • • • • • • • • . • • • • • • • • • • • • 0 11 • • • • • • • • • • • • • • • • • • • • . • • • • 0 12 • • • • • • • • • • • • • • • • • • • • • • • • • 1 13 • • • • • • • • • • • • • • • • • • • • • • • • • 5 14 • • • • • • • • • • • • • • • • • • • • • • • • • 4 15 • • • • • • • • • • • • • • • • • • • • • • • • • 3 43 10

Cl) 7 C)

M :::, to Ci-I 6 (II f"'I f-4 Cl) p. p. :, 5 1M 0 • I 4 o<• Ul M e, p. j t1J 'O d

,-j c.:, 2

0 1 2 3 4 5 6 i 7 8 9 Score of lobes per leaf

Fig.- 14 .. - Scatter diagram for the characters scored f or the Malad population. 44

TABLE19 HYBRID INDEXSCORES IN THE ESCALANTEPOPULATION Plan t Number Scor e P. t r i dent ata • • • • • • • • • • • • • • • • • • • • 0 or 1 Q. Stansbur i ana . • • • • • • • • • • • • • • • • • • 20 or 21 1 • • • • • • • • • • • • • • • • • • • • • • • • • 21 2 • • • • • • • • • • • • • • • • • • • • • • • • • 20 3 • • • • • • • • • • • • • • • • • • • • • • • • • 20 4 • • • • • • • • • • • • • • • • • • • • • • • • • 19 5 • • • • • • • • • • • • • • • • • • • • • • • • • 20 6 • • • • • • • • • • • • • • • • • • • • • • • • • 19 7 • • • • • • • • •• • • • • ... • • •••• • ••• • 20 8 ...... • • • • • • • • • • ...... • 20 9 • • • • • • • • • • •• • • • • • • •• • ••••• • 20 10 • • • • • • • •• • ••• • • • • • ...... •· .. • 20 11 • •• • • • • • • • • • • • • • • • •• ••• •••• • 20 12 • • • • • • • • • • • • • • • • • ...... • 21 13 ...... • • • • • • • • • • ...... • 19 14 • • • • • • • • • • • • • • • • • ...... •. • 20 15 • • • • • • • • • • • • • • • • • ...... • • 21 16 • • •• • • • • • • • • • • • • • • • •• • • • • • • 20 17 • • • • • • • • • •• • • • • • • • ...... • 20 18 • • • • • • • • • • • • • • • • • •• • ••••• • 20 19 • • • • • • • ..., ...... • • • • ••••• • •• • 20 20 • • • • • • • .,. . . . . • • • • • • • • • • • • • 20 20 21 • • • • • • • • • • • • • • • • • • • • • • • • • • 22 • • • • • • • • • • • • • • • • • •• • ••••• • 18 , 20 23 • • • • • • • • • • • • • • • • • • ...... • 45 10

9 0 _E"_f,-"'iOo...... ,q~-I, ''e..., ' ' ' ' 8

G> u 7 f ¥- f fl) 6 CIS ""Q) .... "' t 5 f~f "'4= 0 t • f*t I 4 0'• It (/J \ <" Q) ff "'°t-{ "' ,c; 1"0,( rn 3 ,~x,, . "tJ '~ cu f ....= ' \ t:, ' ' 2

1 2 4 5 6 7 9 Score ef lobes per leaf Fig. 15. - Scatter diagram for the characters scored tor the Escalante population. 46

TABLE 20

HYBRI D INDEXSCORES I N THE KANAB POPULATION Plant Number Score P. tridentata. • • • • • • • • • • • • • • • • • • • • 0 or 1 £•- Stan~buriaua • • • • • • • • • • • • • • • • • • • 20 or 21 1 • • • • • • • • • • • • • • • • • • • • • • • • • 20 2 • • • • • • • • • • • • • • • • • • • • • • • • • 20 3 • • • • • • • • • • • • • • • • • • • • • • • • • 20 4 • • • • • • • • • • • • • • • • • • • • • • • • • 20 5 • • • • • • • • • • • • • • • • • • • • • • • • • 20 6 • • • • • • • • • • • • • • • • • • • • • • • • • 19 7 • • • • • • • • • • • • • • • • • • • • • • • • • 20 8 • • • • • • • • • • • • • • • • • • • • • • • • • 21 9 • • • • • • • • • • • • • • • • • • • • • • • • • 21 10 • • • • • • • • • • • • • • • • • • • • • • • • • 20 11 • • • • • • .. • • • • • • • • • • • • • • • • • • 18 12 • • • • • • • • • • • • • • • • • • • • • • • • • 20 13 • • • • • • • • • • • • • • • • • • • • • • • • • 20 14 • • • • • • • • • • • • • • • • • • • • • • • • • 16 47

10 0 .+ \ b 1'hl'•/-.fion

O> 7 f 'Mi $ot ::s tll CM 6 *f ,..."'GI "4 Q) t 5 f- 0 f *t • t I 4 04• fl.) t *

ti.I 3 'ti

\ I s I I 2 ' I' \ Exh~17o l .. +i •ti I 1

I l 0 6

0 1 2 3 4 5 6 7 8 9 Score of lobes per leaf

Fig, 16 . - Seatter diagram for the chara cters scored for the Kanab population . 48

TABLE21

HYBRIDINDEX SCORES IN THE EDGEMONT POPULATION Plant Number Score , 0 or 1 P. tridenta cta • • • • • • "' • • • • " • • • .. • • • -c. Stansbutiana • • • • > • • It • • • • • .. • • • • • 20 or 21 -l • • • • ,. • • • • • • • • • • • • • • • • • • • • 19 2 • • • • • • • • • • • • • • • • • • • • • • ,, • • 19 3 • • • • • • • • • • • • • • • • 18 • • • • , • • • • • 4 • • • • • • • • • • • • • • • "' • • • • • • • • 18 5 • • • • • • • • • • • • • • .. • • • .. • • • .. • ,, 19 6 • • • • • • • • • • • • • • • • • • • • • • • .. .. 18 7 • .. • • • • • • • • • • • • • • • • • • • • • • • 11 8· • • • • • • • • • • • .. • • • • • • • • • • • • .. 20 9 • • • • • • • • • • • • • • • • • • • • • • • • • 19 10 • • • • • • • • • ·• • • • • • • • • • • • • • • • 18 11 • • • • • • • • • • • • • • • • • • • • • • • • • 19 12 • • • • • • • • • • • • • • • • • • • • • • • • • 20 13 • • • • • • • • • • • ·• • • • • • • • • • • • • , 19 14 • • • • • • • • • • • • • • • • • • • • • • .. • , 19 15 • • • • • • • • • • • • • • • • • • • • • • • • • 18 16 • • • • • • • • • • • • • • • • • • • • • • • • • 18 17 • • • • • • • • • • • • • • • • • • • • • • • • • 19 18 • • • • • • • • • • • • • • • • • • • • • • , • • 18 19 • • • • • • • • • • • • • • • • • • • • • • • • • 20 20 • • • • • • • • • • • • • ·• • • • • • • • • • • • 19 21 • • • • • • • • • • • • • • • • • • • • • • • • • 19 49 10

I I I» u 7 I (ti f ..... ( ( a(Q f I ""11' 6 I ....(I) $.i GI p. p. :, 5 \ ft-4 \ 0 \ • \ ! ' • 4 ' 0" l .,._fio', !IJ ...... ~,.,-oo ,- - t>_ -"' ,.,. ~,, (I) I p. I I CD 3 "0 I Q I ns I I s I 2 t t I

II ( 1 I I I I I I· I .....I 0 Ci

0 l 2 4 5 6 7 8 9 Seore of lobes per leaf Fig. 17,, .. Seatter diagram for the characters scored for the Edgemont population . 50

TABLE22

HYBRID INDEX SCORF.S IN THE SCIPIO PASS POPULATION Plant Number Score P. tridentata • • • • • • • • • • • • • • • • • • • • 0 or 1 -c. S£fU!Sbux-iana• • • • • • • • • • • • • • • • • • • 11 or 12 -1 • • • • • • • • • • • • • • • • • • • • • . • • • 12 2 • • • • • • • • • • • • • • • • • • • • • • • • • 12 3 • • • • • • • • • • • • • • • • • • • • • • • • • 10 4 • • • • • • • • • • • • • • • • • • • • • • • • • 9 5 • • • • • • • • • • • • • • • • • • • • • • • • • 6 6 • • • • • • • • • • • • • • • • • • • • • • • • • 12 7 • • • • • • • • • • • • • • • • • • • • • • • • • 10 8 • • • • • • • • • • • • • • • • • • • • • • • • • 11 9 • • • • • • • • • • • • • • • • • • • • • • • • • 8 10 • • • • • • • • • • • • • • • • • • • • • • • • • 11 11 • • • • • • • • • • • • • • • • • • • • • • • • • 12 12 • • • • • • • • • • • • • • • • • • • • • • • • • 11 13 • • • • • • • • • • • • • • • • • • • • • • • • • 11 14 • • • • • • • • • • • • • • • • • • • • • • • • • 8 15 • • • • • • • • • • • • • • • • • • • • • • • • • 12 16 • • • • • • • • • • • • • • • • • • • • • • • • • 11 17 • • • • • • • • • • • • • • • • • • • • • • • • • 12 18 • • • • • • • • • • • • • • • • • • • • • • • • • 10 19 • • • • • • • • • • • • • • • • • • • • • • • • 0 11 20 • • • • • • • • • • • • • • • • • • • • • • • • • 10 21 • • • • • • • • • • • • • • • • • • • • • • • • • 10 51

(.) u 7

$..t ::s Cll (M ~

0 l 2 3 4 5 6 7 8 Score of lobes per leaf

Fig., 18., - SQatter diagram for the characters scored for the Seipio Pass population . 52

TABLE23

HYBRIDINDEX SCORES IN THE PINE VALLEY POPULATION Plant Number Score P. tr i dentata • • • • • • • • • • • • • • • • • • • • 0 or 1 -c. Stansburiana • • • • • • • • • • • • • • • • • • • 11 or 12 -1 • • • • • • • • • • • • • • • • • • • • • • • • • 10 2 • • • • • • • • • • • • • • • • • • • • • • • • • 11 3 • • • • • • • • • • • • • • • • • • • • • • • • • 10 4 • • • • • • • • • • • • • • • • • • • • • • • • • 0 5 • • • • • • • • • • • • • • • • • • • .- . • • • • 10 6 • • • • • • • • • • • • • • • • • • • • • • • • • 10 7 • • • • • • • • • • • • • • • • • • • • • • • • • 5 • • • • • • • • • • • • • • • • • • • • • • • • • 11 9 • • • • • • • • • • • • • • • • • • • • • • • • • 2 10 • • • • • • • • • • • • • • • • • • • • • • • • • 10 11 • • • • • • • • • • • • • • • • • • • • • • • • • 0 53

10 .

9 0 .A- I

8 I r:.' • 01 '><....'/ \Q'1 0 I \ o-~/ \1) 7 , () ~.,..,,,,,, Ct1 t+-t / f.t :::s flJ t+-t 11$ 6

II) 3 11.! Pt, t-1a CJ 2 I ., { . (', 0 ,~~,...... 1 E'y.f,~f,- cl J.- --

0 ---0-- --.., __ l_..,., __ 2__ ,.... ,,-..-:;--·--4---5---6- ....,..--7--• __8 ___ 9 Score of lobes per leaf Fig ~ 19 , Scatter diagram for the characters scored for the Pine Valley populati (\n. DISCUSSION

Discordant variation occurs in populations throughout Utah and apparently throughout the mountain west whenever Purshia tridentata, Purshia glandulQ-sa, or Cowania Stansbiu-iana come in contact with each other. Since the flowering dates of all three species overlap with each other (Abrams, 1940), introgreseion occurs, apparently, regardless of the direction of elo~ or of other features of the to- pography.

During the investigation of the introgression reported above, it was fot!nd that there is considerable intraplant variation for most of the characters which were studied; this is particularly true of Cowania St~..neburiana. FC\r th.is reason it .i.s important that the magnitude of varia .U on be determined early in the study of population varie.Uol\ so th.at it can be properly distingui .shed from inter- plant variation. I~ many other reported studies of introgression . (Stebbins, 1956; Anderson, 1952; Fassett, 1952; Zobel, 1951) this important feature appears to have been neglected. Of course in some of these studies the intraplant variation may have been of sueh a low magnitude that it was not important to distinguish it. However , in this study intraplant variation was useful not only in determining which characters should be used in analyzing the populations, but also in determining how each character should be scored.

54 55

Population Dynamics In any population that exhibits any degree of variability an extrapolation can be made to the putative type of plants which would have yielded the vari ation found in the population , but unless this variation is due to introgression (discordant variation), the parental types would have had to belong to the same species, subspecies. or variety as the rest of the population . Illustrations of this were found in the Kanab£• Stansburiana population (Fig. 16) and in the Toiyabe f • tr!dentata population (Fig. 2). As shown above (Ta- bles 6 and 20t Fig . 2 and 16) both of these populations are fairly uniform. Tb.e Ka.nab C<.'w9,,niaStansburie.n.a. population if.i especially uniform. Altb.ougb. extrapolates were made, the variation is not discordant; f.herefore, the characteristics of the extrapolates would admit them. to tho same species as the other plan.ts in the population .

In the Toiya .be population all of the variation except the halt-stalked bypantbium glands is within the range of variation al- lowed for Purshia tridenteta. Since other f • trid .entata, popula tions (to be discussed later) have apparently obta.ined stalked bypanthium glands from Cowania Stansburiana , it might b.e supposed that this population has also been introgressed from this species. However , since only one plant in the population sample exhibited this variation, it might be explained on the basis of a new mutation (a rather unlikely explanation), or on the basis of variable penetrance of these genes in the Cowania-J'urshia populations . Since f • td.denta£e and£• Stan,sburiana are apparently quite closely related• and since they seem to hybridize readily whenever they come in contact with 56 each other, it is possible that they differ primarily in accumulated modifying genes . It is conceivable then that both species may possess genes for stalked hypanthium glands • but that f • tridentata also possesses suppressor genes for the glands which under certain mi• croenvironmental conditions may be rendered ineffective. Of course, as noted above, stalked hypanthium glands could have resulted from introgression, but more than one plant out of twenty-two would gen - erally exhibit discordant variation if this were the case. In several of the populations and subpopulations the extrapolates suggest that the parental population types were similar to pure£ • Stansburiana. and pure.!! • tridentata. This was true in the Kanosh population and in the Oak City subpopulation in which pure f • tridentata appears to be introgressing into£• Stansburiana; and in the other Oak City subpopulation, Pocatello population , and Malad population in which£• Stansburiana appears to be introgressing into !!• tridentata. In other populations and subpopulations the extrapolates suggest impure£• Stansburiana-like and impure f • tridentata•like pa - rental types. The variation of these putative parental -types from the pure species is most easily explained on the basis that they themselves are introgressed, since in many cases it appeared that £.• St!B§burian~ and f • tridentata had exchanged a character or a group of characters. In the populations from Edgemont , Scipio Pass, and Escalante and in the Dividend subpopulation, introgressed Purshia tridentata plants appear to be introgressing into£• Stansburiana populations that had previously been introgressed. In the popula - tions from Helena , Polson, and Dubois and in the Dividend and Cove 57 Fort subpopulations, introgressed £• Stansburiana plants appear to be introgressing into f• tridentata populations that had been previously introgressed.

At Cove Fort a type resembling f.• glandulosa appears to be introgressing into pure£• Stall$buriana, while at Pine Valley pure !!• glandulosa appears to be introgressing into an introgressed £• Stansburiana subpopulation and a pure Purshia tridentata subpopulation. Several populations were deliberately collected in such a manner as to give divergent subpopulations. As stated above the two subpopulations at Pine Valley appear to have their discordant variability from the same source, Purshia glapdulosa. One Dividend subpopulation and one Oak City subpopulation or f• tridentata appear to have received their discordant vari ation from the£• Stansburiana plants in the area, and, vice versa, the£• Stansburiana subpopula• tions appear to have received their discordant variation from E!!!':- shia tridentata plants in the area. At Cove Fort there are two populations which have discordant variation. One of these. Cowania Stansburiana, appears to have been introgressed with f• glandulosa. The other population, Purshia tridentata, appears to have been produced from hybridization of populations which were themselves introgressed. One extrapolate of this latter population appeared to be£• Stansburiana introgressed with f. triden .tata, while the other extrapolate appeared to be ~- !.!.!!.! tridentata introgressed with£• Stansburiana. Since the extrapolated introgressed £• Stansburiana had no hypanthium glands it probably represents a different population than the present intro- 58 gressed £• Stansburiana. The White Mountain population #1 has the morphological characteristics of Purshia glandulosa. Since the extrapolates were simi• lar to introgressed f • tri dentata and introgressed £• Stansburiana, and since the hybrid index scores show that the population is more

Purshia-like than Cowania-like, ~- glandulosa has apparently been produced by the hybridization of introgressed .f• tridentata with introgressed £• Stansburiana followed by backcrossing to the introgressed E• tridentata before the plan ts appa rently became stabilized hybrid segregants.

In the White Mountain population #fJ. E• glandulosa has considerable variation due apparently to introgression from populations which themselves possess considerable discordant variation. One of these extrapolates suggests a f.• glandulosa population which has pu• besceat upper leaf surfaces and high glandulosity of the leaves, and therefore. probably represents a population off• glandulosa introgressed with both£• Stansburiana and E.• tridentata. The other extrapolate has characteristics which suggest a£• Stansburiana pop • ulation introgressed with f • tridentata. The extrapolates of the Motoqua population of!• glandulosa have apparently been introgressed themselves. One of the extrapolates resembles!• glandulosa introgressed with£• Stansburiana . It was not possible to determine from the analysis whether the sec~ ond extrapolate was introgressed !!• tridentata or introgressed Cowania alba Goodding. (According to Rydberg (1913) £•~might be a hybrid type itself.) The present population is probably the

result of continued backcrossing of the F1 between populations sim- 59 ilar to these extrapolates onto the introgressed Purshia glanduloaa plants.

Origin of Purshia glandulosa It appears that the ultimate taxa involved in the production of?• glandulosa were f• tridenta£a and£• Stansburiana. This was probably initiated by hybridization of!!• tridentata and Cowania

Stansburiana followed by baekcrossing in both directions to yield introgressed f• trideptata and£· Stansburiana populations. Subse- quently these introgressed populations hybridized and with subse• quent baekcrossing to the introgressed f• tridentata population yielded types si~ilar to~• glandulosa. Although no plants were grown from seed in this study to determine for certain that this species (f. glandulosa) can reproduce itself, the seeds which were examined were found to be plump which would suggest that they are viable. The fact that these forms oecttr in sizeable uniform populations also indicates that the plants are sexually fertile. With such an origin f• glandulosa could very well appear in different places simultaneously arid at different times. However, since !J!!:- shia glandulosa is characterized by rather distinct characters, this should not be construed to mean that any stabilized hybrid segregant involving f• tridentata and£• Stansburiana is f• glandul~sa. Other combinations of characters arising in a similar manner could conceivably result in other species. Combinations of characters that are only slightly different from the described E.• glandulosa and \Vhose entities share in the f.• glandulosa gene pool could be considered subspecies of£.• glandulosa. This is possibly the case of the 60 White Mountain population #2 and of the Motoqua population. Combi- nations of characters that are different from the described species off• &.landulosa and whose entities are at present involved in a gene pool different from that off• glandulosa, and are isolated and breeding true might conceivably be considered a different species. Since Purahia tridentata, Purshia glandulosa, and Cowania Stansburiana do hybridize readily, it might be appropriate to con- sider the two genera, Cowania and Purshia, as one genus and the different forms as species within that genus.

Location 2.! Parental Tues In ,nost eases the parental types, or plants similar to the parental types, were found either in the immediate vicinity o1 the introgressed population (sometimes they were in the population sample), or they were known to occur within the same general region. This l1ttter situation was true in both White Mountain populations where!!• tridentata•like plants characterized one of the extrapo• lates, and in the Escalante population in ,vhich £• Stansburiana-like plants were extrapolated. In some cases the pa.rental types have not been reported for the particular area in question. One such ease is at Cove Fort where the extra polated parent rese mbles f• glandulosa. However, since f• glandulosa is found in the same vegetation zone as the Cove Fort po pulation. and since Cove Fort is located only about seventy- five miles from southern Nevada, an.area from which£• glandulosa has been reported, it appears to be very possible that a few Furshia glandulosa-type plants might be found in the Cove Fort vicinity if 61 a seareh were made for them. There are no great mountain ranges or other natural barriers to prevent the spread off• glandulosa from southern Nevada to Ut_ah,. However , sinee as mentioned above, there is a good possibility that Purshia glandulosa may arise independent- ly at several points in time and space, it is conceivable that it could appear in the Cove Fort vicinity without having come from Ne- vada. It is also possible that although no f• glandulosa-type plants might currently be found in the Cove Fort vicinity, they may have existed there at some time in the past, and at that time fur• nished the variation whieh is still present in this population .

Five other eases in which a parental type exactly comparable to the extrapolate is not present in the immediate area are found at Malad , Pocatello, Dubois , Helena , and Polson in which Cowania

Stansburiana , one of the putative parents , has not been reported for

Idaho nor for Montana . Since Malad and Pocatello are located only about twenty miles and sixty miles respectively from Utah where £• Stansburiana is abundant , it is possible that a tew stray plants may be found around these areas if a search were made for them. Or it may be that former populations of£• Stansburiana in the Malad and Pocatello areas are now extinct. There is also the possibility ot introgreasion proceeding step-wise from one population to another from Utah to Idaho,. However, since the distance is great between the populations at Dubois , Helena , and Polson , and the area for which Cowania St(Ul$buriana has been reported, and since several mountain ranges form natural barriers for this southern species; it is unlikely that pure£ • Stansburiana would be found this far north. It is conceiv- 62 able that introgression may have proceeded north in a step - wise

fashion or that produ cts of hybridization many miles away may have n1igrated north to produee the discordant variation found in these populations . It is possible , however , that£ • Stansburiana could have been present at some time in the past when the mountains were lower and the climate warmer. This situation apparently occurred in the Tertiary period of the Cenozoic era . How9ver, as suggested by

Anderson (1952) , when introgression confers a strong selective advantage on some of the mongrel ottspring , they and their descendants may spread outside the immediate area in which hybridization occurred . This being true mongrel Cowania Stansburiana may at the present time be found in some ot the upper mountain slopes around Dubois , Helena , and Polson , and is furnishing variation to the Pur- shia populations of these areas .

Evolution in Purshia triden .tata In the Oak City and Pocatello populations stalked hypanthium glands are apparently introduced into f • tridentata from Cowania Stansburiana•type plants . However , many of the individuals in the f • tridentata populations that were collected outside the distribu - tional range of Cowapia Stansburiana exhibited these same charae• ters . The introgressive segment for these characters of stalked hypanthium glands may have spread by means ot the above mentioned mon"" grel offspring . It is also conceivable that these eharacters could spread from one P. tridentata population to another from within the - " zone of P. tridentata-c . Stansburiana overlap to the area outside -- . ... the zone of overlap , in which caae such a population as that at 63 Malad which is near the zone boundary would be a key population in introducing the characters into populations at a greater distance from this zone. This may mean that the Dubois, Helena, and Polson populations could very well have received stalked hypanthium glands from some mongrel C. Stansburiana directly, or indirectly from one - . f• tridentat9 population to another. Since stalked hypanthium glands appear to be spreading to f!!!:- shia tridentata populations, they probably have considerable survival value. No attempt was made to assess this survival value, but it may be that the glands furnish protection for the fruit and seeds against insect attack. It is also conceivable that the presence of these hypanthium glands might be responsible for the low palatabil ... ity of some of the!• tridentata populations reported by the Forest Service (1937). Under the selective pressures which have been ex- erted by heavy grazing off• tridentata in these areas during the last century. such unpalatability could conceivably render a distinct selective advantage to those plants possessing this characteristic. CONCLUSI ONS

From detailed. analyses of variation toW'ld in populations of

·cowapia and Purshia it has been possible to interpret patterns of gene flow in these populations. Hybridization followed by back- eroasing appears to occur whenever J>ursh,i.a tridenta\a, Pu[$hia glM- dulosa, and Cowpia Stansbul'.'iana come in contact with eaeh other. Thi.$ results in discordant variation whi¢h appears to be rampant throughout the mountain west in these s pecies.

Purshia glandulosa is apparently a stabilized hybrid segregant resulting from the introgression of£• Stan1buriana•type characters into!!• tridentata-type plants. Since f• t[ident a~a and Cowanis Stansbur&ana occur sympatrically in many sites throughout the Great

Basin, and. since hybridization is common whenever they a.re sym- patric, it is likely that stabilized segregants have been formed at different times and at different geo graphic locations. On this as- sumption it is very likely that different f• glandu~os~ populations may have had independent origins.

Through introgression Purshta tridentata appears to be aequir• ing stalked hypanthiwn glands from Cowania Stansburtruui. This de• vel&pment, appears to be a recent trend in the evolution of Purshia tridentate•

64 REFEUENCES

Abrams, Leroy. 1940. Illustrated flora of the Pacific States. II:

407-451. Stanford, California: Stanford University Press .

Anderson, Edgar. 1949. Introgressive hybridization, PP• 1-102.

New York: John Wiley and Sons, Inc. ----· 1951. Coneordant versus discordant variation in relation to introgression. Evolution 5: 133-141. ---- , and Amy Gage. 1952. Introgressive hybridization in Phlox bifida. American Journal of Botany 39: 399-404. Benson, Lyman, and Robert A. Darrow. 1954. The trees and shrubs of

the southwestern deserts, pp. 142•144. Tucson and Albuquer -

que: University of Arizona Press and University of New Mexico Press . Fassett, Norman c., and Barbara Calhoun. 1952 . Introgression between TYpha latifolia and!• angustifolia. Evolution 6: 367-

379.

F'orest Servi ce. 1937. Range plant handbook, PP• B68, 69, Bl16. Washington, D.C.: United States Government Printing Off ice.

Kearney , Thomas H., and Rabert H. Peebles . 1942. Flowering plants

and ferns of Arizona, pp. 405, 408. Washington , D.C.i United States Government Pr intin g Office . Lynch, F. c. c. 1924. Map of southern portion of Dominion of Can- ada indicating vegetation and forest cover. National Re-

65 66

sources Intelligence Service of the Depar tment of the Interior

(Canada).

McMinn, Howard E. 1951. An illustrated manual of California shrubs,

PP• 202-204. Berkeley and Los Angeles: University ot Califor- nia Press. Peck , .Morton E. 1941. A manual of the higher plants of Oregon, P• 406. Portland1 Binfords and Mort.

Preston, Richard J., Jr. 1940. Rocky Mountai n Trees,, pp . 184, 185. Ames: Iowa State College Press . Rydberg, Per Axel. 1913. Rosaeeae . North American Flora 22(3):

239-240, (5): 399-418.

Shantz , H. L., and Raphael Zon. 1923. Natural veget .ation (map).

Washington, D.C.: Bureau of Plan t Industry and the Forest

Service, United States Departmen t of Agri culture. Stebbins, G. Ledyard, and L. Ferlan. 1956. Popu lation variability, hybridigation, and introgression in some species of OJ?hrys. Evolution 10: 32-46. Wooton, E,. o., and Paul c. Standley. 1915. Flora of New Mexico, p. 318. Washington , o.c.: United States Government Printing Of- fi .ce. Zobel , Bruce. 1951. The natural hybrid between Coulter and Jeffrey

Pines . Evolution 5: 405-413. ABSTRACT

A study ot discordant variation in populations of Purshia trt ... dentata, Ptll"shia gland11losa, and Cowania Stansburiana has disclosed that introgressive hybridization ean be expeeted whenever these spe - cies come in contact \Vith each ot her. The introgression is not only of one pure sper.ies into t hat of another, but is also of introgres• sed populations into other introgressed populations and of pure pop - ulations into introgressed populations.

Evidence was found showing that in all probability Purshia glandulosJ1 is a stabilized segregant derived from introgressed pop - ulations. Evidence was also found and presented to show that introgression is responsible for the recent acquisition of stalked hypan - thium glands by many ~opul ations of Purshia trid~ntata .