Table Of ContentMadrono, Vol. 47, No. 1, pp. 21-28, 2000
CHROMOSOME COUNTS AND TAXONOMIC NOTES ON
DRABA (BRASSICACEAE) OF THE INTERMOUNTAIN WEST
1:
UTAH AND VICINITY
Michael D. Windham
Utah Museum of Natural History, University of Utah, Salt Lake City,
UT 84112-0050
Abstract
Of the 350+ species ascribed to Draba, nearly one quarter occur in the Intermountain Region of the
western United States. Most of these Draba species have not been examined cytologically. This paper
presents a total of 18 chromosome counts for 11 different taxaoccurring in Utah, Wyoming, andArizona.
The chromosome numbers of D. juniperina, D. kassii, D. maguirei var. maguirei, D. rectifructa, D.
sobolifera, D. spectabilis var. spectabilis, and D. subalpina are reported here for the first time. Counts
differing from published reports are documented for D. asprella var. stelligera and D. cuneifolia var.
cuneifolia. The taxonomic significance of the new chromosome counts is discussed for each species.
Counts of n = 11 and n = 13 appear to be the first reports of those numbers in the genus, and they
complete the continuous series of aneuploid base numbers extending from 8 to 16. It is suggested that
the Intermountain West may be a center of diversity for aneuploid Draba, and that this assemblage of
species provides a unique opportunity to study chromosomal evolution and speciation.
Species assigned to Draba, considered to be the a combination of chromosome number, flower col-
largest genus in the Brassicaceae (Rollins 1993), or, breeding system, and hybridization studies.
occupy a variety of habitats and occur on all con- All 17 of the white-flowered species studied by
tinents except Australia and Antarctica. The group Mulligan exhibit euploid chromosome numbers
achieves its greatest diversity in topographically based onx = 8. They clearly are relatedto Eurasian
complex, mountainous regions where the disjunct boreal species assignedby Schulz (1927) tothe sec-
occurrence of suitable habitats seems to favor iso- tion Leucodraba DC. Another nine Canadian spe-
lation and speciation (Payson 1917). A prime ex- cies were assigned to his yellow-flowered euploid
ample of this is seen in the Intermountain Region alliance, which also frequents boreal habitats and
of the western United States, broadly defined here has representatives in Eurasia. The remaining 13
as the territory extending from the continental di- Canadian taxa were placed in a yellow-flowered
vide to the Pacific Crest (Sierran-Cascade axis). Of group characterized by aneuploid chromosome
the 350+ species attributed to Draba by Rollins numbers of« = 9, 10, 12, 14, 15, and 37 (Mulligan
(1993), nearly one quarter occur in this region and 1976). Apparently restricted to North and South
masoTrtheheethcIaynnttoe5lrom0go%yunootffaitDnhroWaseebsaatrieissectnoednrecraemriincnecdto.ogniOti.ftatahse f5a7r Atmomulecerrhiacnotaf,otfthhetihsweeaswstaserermmn/bdlUarngyietceoodfndSsitpatetiecosin.esstahaptpeparresvamilorien
Mulligan's (1976) informal classification of
taamxianecodnfcihnreodmotosotmhaisllrye.gioHna,lfonolfy t1h1esheavaerebekennoewxn- North American Draba is a vast improvement over
the patently unnatural sections proposed by Schulz
from single counts, and none can be considered ad-
equately sampled. By comparison, 37 of the 40 u(1a9t2e7d).phyHloowgeevneert,icaitllcyanuntnielitthheercbheroumseodsonmoer nevuaml--
Draba species found in Canada and Alaska have bers of local Draba species have been determined.
been studied cytologically, thanks in large part to The goals of this study were: 1) to collect crucial
the diligent efforts ofG. A. Mulhgan (1966, 1970a, chromosome data for Intermountain Draba species,
b, 1971a, b, 1972, 1974, 1975, 1976). 2) to critically assess current taxonomic treatments
Mulligan's work on the high-latitude North for the species sampled, and 3) to develop a set of
American species of Draba (summarized in the chromosomally vouchered samples for a DNA
1976 paper) led to major advances in our taxonom- analysis (Beilstein and Windham in prep.) designed
ic understanding of the genus. In addition to clari- to test the monophyly of Mulligan's (1976) infor-
fying species boundaries in several groups, his data mal species groups.
provided the basis for the only modem infrageneric
classification of North American Draba. Setting Materials and Methods
aside Draba (Erophila) verna L., a Eurasian intro-
duction unrelated to the native species. Mulligan Chromosome counts were made from flower
(1976) recognized three informal groups based on buds of wild plants fixed in Farmer's solution (3
MADRONO
22 [Vol. 47
parts 95% ethanol: 1 part glacial acetic acid). Fixed surprised when samples from two widely separated
materials were stored at -20°C for up to five years Utah populations yielded counts ofn = 12 (Fig. 1)
and transferred to 70% ethanol immediately before and 2n = 24. These determinations agree with pre-
making slides. Buds (or dissected anthers in larger- vious reports forD. albertina, including fourcounts
flowered species) were macerated in a drop of 1% from Alberta and one from the Northwest Territo-
acetocarmine stain, which was mixed 1:1 withHoy- ries (Mulligan 1975). An additional count of n =
er's solution prior to setting the cover slip and 12 from Wyoming originally attributed to D. sten-
squashing. Slides were examined with an Olympus oloba (Mulligan 1966) was reassigned to D. alber-
BH-2phase contrastmicroscope, andrepresentative tina in a subsequent paper by Mulligan (1975).
cells were photographed using Kodak Technical Prior to detailed studies of the group (Mulligan
Pan 2415 film. A full set ofvoucher specimens was 1975), Draba albertina was treated as a synonym
deposited at the Garrett Herbarium, Utah Museum or variety (nana) ofD. stenoloba. Afterdiscovering
of Natural History (UT). Duplicate vouchers were that the two taxa had different chromosome num-
deposited at the herbaria listed in Table 1. To guide bers. Mulligan recognized them as separate species
the discussion, I produced a compendium of pub- based on correlated morphological and geographi-
lished chromosome counts for all taxa studied and cal differences. The decision to classify these taxa
their putative relatives. This list was assembled by as species also is supported by artificial hybridiza-
running all accepted names and synonyms from tion experiments (Mulligan 1975), which indicate
Rollins (1993) and Kartesz (1994) through Chro- that any hybrids formed are completely sterile.
mosome Numbers of Flowering Plants (Federov According to Mulligan (1975) and Rollins
1974) and a complete set of the Index to Plant (1993), D. stenoloba, with a chromosome number
Chromosome Numbers spanning the period 1966- of = 20 and mostly dendritic trichomes on the
1995 (Omduff 1967, 1968; Moore 1973, 1974, upper leaf surfaces, is rarely encountered south of
1977; Goldblatt 1981, 1984, 1985, 1988; Goldblatt the Canadian border. They assign most collections
and Johnson 1990, 1991, 1994, 1996 & 1998). The identified as D. stenoloba from the western United
primary literature was consulted to verify critical States to D. albertina, characterized by a chromo-
taxonomic and geographic information for each some number ofn = 12 and simple or once-forked
North American count identified by this search. adaxial leaf trichomes. My morphological studies
ofUtah specimens concur that typical D. stenoloba
Results is not present in the state, and all collections iden-
My chromosome studies ofUtah, Wyoming, and tified as such represent D. albertina. Both taxa be-
long to Mulligan's (1976) yellow-flowered aneu-
Arizona Draba species yielded a total of 18 counts
ploid group.
for 11 different taxa (Table 1). Seven ofthese taxa Draba asprella, a species endemic to Arizona
jhuanviepenroitnabeeDnocmou{nnte=dpr1e1)v,ioDus.lyk.asTshieisWeeilnschlud{enD—=. caonldlescotuitohnesrannUdtaah,coinsfruespirnegsecnhtredomboysfoemwehleirtebraartuiruem.
sb11po16el)),,citfDaeDbr..ialmriRaesycgdt{ubinif.rr—eu{cint1a0C=).,C.1La3.n)Ld,.HiDDHt..icthssccpuh.ebcca.vtlaarp{b.ininlmai=asgGGu1oir2o)re,deeimnDea.{nnvsaor&-. ANCliuotmcesbroianentgriulrsnee.ocaoTCnuohd.ni,tstoAchfoeZunnIstn=tdudede±xire1eisd6vebstayopfprRPeoolalarmlnsitanisnpCohtaphrnuedolampRtroiiisiomdonaemrniey-n
C. L. Hitchc. {n = 13). Counts for two of the re- berg (1971), which was not identified to variety in
maining taxa, D. asprella Greene var. stelligera O.
E&. GS.chvualr.zc{unne—ifo1l5i)a, (annd=D1.5)c,undiefiffeorlifaroNumttn.umebx.erTs. ptchaoeruenntotrltiyogivnuaanrl.doapcsapupremerel.nltaReoadlnldicnorsuenpot(r1t9os9f3a)nn aa=dtdtir1ti6ibountfeaoslr,vtaahpri-.s
previously reported in the literature. Unexpected stelligera. The latter count is critical because it
counts, especially those that disagree with the lit- seems to place D. asprella in Mulligan's (1976)
eurraetsure1,-6.areDetdeorcmuimneanttieondspohfotogr=aph1i1caalnldy «in=Fi1g3- cyoeullnotwo-fflnow=ere1d5 e(uFpigl.oi2d) awsosuelmdblsauggeg,eswthearneaafsfilmiay-
tahpepegaernutso,baendthtehefyirsctomrepploerttes tohfetchoonsteinnuuomubsesresriiesn tion with his aneuploid group. I amconfident ofmy
ofaneuploid base numbers extending from 8 to 16. dfertoemrmeiingahttioinn,divwihdiucalhs.isAbtatsheids pooninatt, lIeaasmt 4in0clcienlelds
In fact, this small sample of taxa includes every
step in that aneuploid series except n = 9 and n = to discount the undocumented euploid report and
assignD. asprella to the yellow-flowered aneuploid
14.
group. In the upcoming field season, I hope to ob-
tain accurate counts for all four varieties and de-
Discussion
termine whether var. stelligera is truly polymorphic
The plants herein referred to Draba albertina with regard to chromosome number.
Greene originally were identified as D. stenoloba The available literature provides two chromo-
Ledeb. based on the treatment in A Utah Flora some counts for Draba cuneifolia. Rollins and Rii-
(Welsh 1993). Because D stenoloba has a chro- denberg (1971) report acount ofn= 16 fromPecos
mosome number ofn = 20 (Mulligan 1975), I was Co., TX. Althoughnotidentifiedtovariety,thiscol-
2000] WINDHAM: CHROMOSOME COUNTS ON DRABA 23
Table 1. ChromosomeCountsonDraba fromUtahandVicinity. Countsdifferingfrompreviouslypublishedreports
are marked by an asterisk. Apparent first counts for a taxon are marked by a double asterisk following the relevant
JnTame=.JLaemtetesrsThbeerfroireen;coWllec=tiMoincnhuamebleWrisniddhenatmi;fyTthWe f=olTlhoewriengsacoWlilencdthorasm:;EMRE=WEr=icMRairckiaartW;iRnSdh=amR;.MDoKugWla=s SMtoolnley;
Windham. Herbaria housing voucher specimens are identified by upper case abbreviations (based on Holmgren et al.
1990) following the collection numbers.
Draba albertina Greene
2n = 24 UT Emery Co. in South Hughes Canyon on the Wasatch Plateau (T14S, R7E,
S30); W & ER 95-185 (UT)
12 UT Salt Lake Co. E ofGuardsman Pass along State Route 152 in the Wasatch
W
Mts. (T2S, R3E, S25); 98-320 (MO, NY, UT)
Draba asprella Greene var. stelligera O.E. Schulz
n = 15, 2« = 30* AZ Coconino Co. along tributary ofBear Wallow Canyon E of Sedona (T17N,
R6E, SIO); W 95-250 (ASU, BRY, COLO, UT, UTC); W,
TW & MKW98-002 (MO, NY, UT)
Draba cuneifolia Nutt. ex Torr. & A. Gray var. cuneifolia
15* AZ Yavapai Co. WNW of Sedona on the SW side ofFay Canyon (T18N, R5E,
S30); W, JT & MEW97-005 (MO, UT)
15* UT Washington Co. NE ofPinto on low hills overlooking road to Cedar City
(T37S, R15W, S26); 99-008 (MO, UT)
Drabajuniperina Dorn**
n = n UT Daggett Co. along Browns Park-Clay Basin road in upper Jesse Ewing Can-
W
yon (T2N, R24E, SI); 96-152 (MO, NY, UT)
11 UT Daggett Co. along State Route 44 on N side of Spring Creek (T2N, R20E,
S\9);W 99-073 (COLO, MO, UT)
WY
11 Sweetwater Co. just E of Richards Gap at S edge of Red Creek Basin (T12N,
R105W, S22); W00-012 (ASU, BRY, MO, UT)
Draba kassii Welsh*'
n = 11 UT Tooele Co. in Goshute Canyon on E slope ofthe Deep Creek Range
(TIOS, R18W, S36); W 98-211 (ASU, COLO, MO, NY, UT)
Draba maguirei C.L. Hitchc.** var. maguirei
16 UT Cache Co. SE slope ofMt. Magog in the Bear River Range (T14N, R3E);
W95-161 (ARIZ, ASU, BRY, COLO, CPH, DAO, ISTC,
MO, NY, OGDF, UC, US, UT, UTC)
Draba nemorosa L. var. nemorosa
UT Summit Co. N base ofWindy Ridge on NE slope ofthe Uinta Mts. (T2N,
R19E, S24); W 99-072 (COLO, MO, NY, UT)
Draba rectifructa C.L. Hitchc'
12 UT Juab Co. N ofMount Nebo near head of Gibson Creek (TlIS, R2E,
W
SI9); 96-204 (UT)
Draba sobolifera Rydb.**
n = n UT Piute Co. S side ofBullion Canyon in the Tushar Mts. (T28S, R5W,
Sll); W cfe /?5 95-201 (ASU, BRY, COLO, MO, NY, OGDF,
UT)
Draba spectabilis Greene var. spectabilis**
n = 10 UT San Juan Co. SE ofGold Basin in the La Sal Mts. (T27S, R24E, S15); W95-
170 (ASU, BRY, COLO, CPH, MO, NY, OGDF, UT, UTC)
W & ER 97-188 (ISTC, UT)
10 UT San Juan Co. NW slope of South Peak in the Abajo Mts. (T34S, R22E);
W95-182 (ASU, BRY, COLO, CPH, MO, NY, OGDF, UT,
UTC)
Draba subalpina Goodman & C.L. Hitchc.**
13 UT Garfield Co. along tributary ofRed Canyon on the Paunsaugunt Plateau
(T36S, R4V2W, SI); W & MKW 92-037 (COLO, MO, UT);
W 96-036 (DAO)
13 UT Garfield Co. near headwaters ofCoyote Hollow on the Paunsaugunt Plateau
(T36S, R4V2W, Siy,W 98-129 (MO, NY, UT)
13 UT Iron Co. NW slope ofBlowhard Mtn. on the Markagunt Plateau (T37S,
R9W, S15); W 92-135 (BRY, MO, NY, UT, UTC)
MADRONO
24 [Vol. 47
2
P
3 4
' 0 e
^^^^ "
%
0
6
Q
Figs. 1-6. Meiotic chromosome squashes for various Draba species. Solid spherical bodies in Figs. 1, 4, and 6 =
nucleoli. Arrows identify overlapping pairs. 1. Diakinesis in D. albertina (n = 12). 2. Late diakinesis in D. asprella
van stelligera (n = 15). 3. Metaphase I in D. cuneifolia var. cuneifolia (n = 15). 4. Diakinesis in D. juniperina (n =
11). 5. Late prophase II in D. maguirei var. maguirei {n = 16 at each pole). Faint spherical body near the center of
each cluster = nucleolus. 6. Diakinesis in D. spectabilis var. spectabilis (n = 10).
lection is presumed to represent var. cuneifolia real. It is interesting to note that my counts derive
based on geographic location. Hartman et al. (1975) from the northwestern portion ofthe species distri-
also report n = 16 for a collection of the typical bution, whereas the two reports ofn = 16 represent
variety from Dallas Co., TX. Given this history, I the southeasternportion ofthe nativerange. Further
was surprised to obtain clear preparations of = sampling is needed to determine whether chromo-
15 (Fig. 3) for two populations ofD. cuneifolia var. some number truly is correlated with geography in
cuneifolia from Arizona and Utah. These counts D. cuneifolia. Such an investigation also shoulden-
were confirmed in at least five cells from three dif- compassDraba reptans, (Lam.) Fern, whichiscon-
ferent plants in each population, so it seems likely sidered closely related (Hitchcock 1941) or inter-
that the apparent chromosomal polymorphism is gradient (Welsh 1993) and apparently displays par-
2000] WINDHAM: CHROMOSOME COUNTS ON DRABA 25
allel variation in chromosome number (Mulligan tween D. oligosperma (x = 8) and D.juniperina (x
1966; Love and Love 1982). Although D. reptans = 11) is not trivial. The former is not a simple
is placed in the aneuploid group by Mulligan polyploid derivative of the latter and, if Mulligan
(1976), the taxon is white-flowered and probably (1976) is right in his assessment of relationships,
should be assigned to a separate group (Beilstein they may belong to different major lineages. The
personal communication). two taxa are easily distinguished using the charac-
Draba juniperina is endemic to pinyon-juniper ters hsted by Dom (1978) and Lichvar (1983), even
woodlands at the northeastern edge of the Uinta where their ranges overlap. Even if they grew to-
Mountains near "Three Comers", the point where gether, which they apparently do not, there would
Utah, Wyoming, and Colorado meet. The taxon, be no opportunity for hybridization because D. oli-
long thoughtto be related toD. oligosperma Hook., gosperma is apomictic and apparently does notpro-
because of the shared occurrence of doubly pecti- duce functional gametes (Mulligan and Findlay
nate trichomes, has a complex nomenclatural his- 1970). All of this provides a strong argument for
tory. It was first separatedfromthe yellow-flowered maintaining Drabajuniperina as a distinct species.
£). oligosperma underthe name D. pectinipila (Rol- Draba kassii is a very rare species endemic to a
lins 1953), a taxon typified on white-flowered spec- few canyons in the Deep Creek Mountains ofwest-
imens from alpine habitats in northwestern Wyo- em Utah. Its relationships are obscure, with Rollins
ming. Dom (1978) pointed out that the petals ofD. (1993) stating that it "is not closely enough related
pectinipila truly are white, but the flowers of pop- to any known species ofDraba to allow inferences
ulations from southwestern Wyoming and north- as to its phylogeny." Comparisons have been
eastern Utah are yellow when fresh. Additional drawn to D. asprella (Welsh 1986b) and D. stan-
morphological features were found tocorrelate with dleyi J. F Macbr. & Payson (Rollins 1993), though
flower color, geography, and habitat, which led both authors suggest that the similarities may be
Dom (1978) to describe the Uinta populations as a superficial. Chromosome numbers have the poten-
new species, D. juniperina. tial to play a cmcial role in determining the rela-
Subsequent studies by Lichvar (1983) seemed to tionships ofthis species. At least 20 cells from five
reinforce thedistinctions amongD. oligosperma, D. different plants clearly establish that the chromo-
pectinipila, and D. juniperina but, in his most re- some number ofD. kassii is n = 11 (Table 1). This
cent work, Rollins (1993) abandoned this taxono- number, which establishes the taxon as a member
my. Stating that designating "deviant types as in- of Mulligan's yellow-flowered aneuploid group,
dependent taxa . . . has done little to clarify the na- would seem to mle out a direct phylogenetic link
ture of the species as a whole" (Rollins 1993), he to D. asprella (n = 15, 16?). The possibility of a
once again synonymized the segregate taxa under relationship to D.juniperina, the only other species
D. oligosperma. Kartesz (1994) followed suit, known to have n — 11, is intriguing. However, the
though Welsh (1986a) maintained juniperina as a two taxa do not appear closely related morpholog-
variety ofD. oligosperma withoutfurthercomment. ically, and any hypothesis of relationships will re-
There has been little use ofthis combination, how- main speculative until additionalDraba species (in-
ever, because var.juniperina is described as having cluding D. standleyi) have been sampled chromo-
"petals evidently white" (Welsh 1993), a character somally.
state not found in Utah specimens. The phylogenetic affinities of Draba maguirei
The chromosome counts presented here for Dra- are as contentious as those of D. kassii, and it ap-
bajuniperina (Fig. 4) provide valuable insight into pears that no recent author has ventured to discuss
the taxonomy of this contentious species complex. its possible relationships. On first describing the
SgettutdiCeos.,atUtTwoanwdidoenleyssiteepairnatSewdeeltocwaaltiteiresCoi.n,DWagY- ssptreickiiensg, aHnidtcqhuciotcekun(l1i9k4e1)ansytatoefdtthheatotihter"iDsravbearsy
revealed that D. juniperina is a sexually-reproduc- from its immediate vicinity. Its closest relatives are
ing taxon with a chromosome number of n — 11. probably those of the ventosa group .". Of the
. .
This is one of two numbers not previously docu- eight taxa comprising Hitchcock's ventosa group,
mented in Mulligan's (1966, 1976) aneuploid se- chromosome counts have been published for two
ries, and clearly establishes this taxon as a member {D. ventosa Gray andD. ruaxes Payson & St. John)
ofthe yellow-flowered aneuploid group. Draba oli- and a third {D. sobolifera) is reported here. All
gosperma, on the other hand, is an apomictic taxon three belong to Mulligan's (1976) yellow-flowered
(Mulligan and Findlay 1970) with three reported aneuploid group with chromosome numbers based
chromosome numbers: 1) 2n = 32 from Alberta on X = 12 and 13. Thus, it is surprising to find that
(Chinnappa and Chmielewski 1987), 2) 2n = ±60 D. maguirei var. maguirei shows a euploid count
from Wyonung (Rolhns 1966), and 3) 2n = 64 of n = 16 (Fig. 5). Additional chromosome counts
from seven populations in Alberta and one in Yu- on D. maguirei and other members of Hitchcock's
kon Territory (Mulligan 1972). These numbers in- ventosa group are needed to resolve this apparent
dicate that D. oligosperma belongs to Mulligan's conflict.
(1976) yellow-flowered euploid group. Draba nemorosa L., a species ofwidespread oc-
The difference in chromosome base numbers be- currence in both North America and Eurasia, was
MADRONO
26 [Vol. 47
assignedby Mulligan (1976) tohisyellow-flowered of n = 10 and point out the need for further sam-
euploid group. All populations analyzed chromo- pling to determine the relationships and propertax-
somally have shown ^ = 8, regardless ofgeograph- onomy ofD. spectabilis.
ic origin. In North America, there have been four Draba subalpina generally is restricted to a sin-
counts from Alberta (Packer 1964; Mulligan 1966, gle geologic stratum, the Claron Formation of
1975), one from Manitoba (Love and Love 1982), Bryce CanyonNational Parkandvicinity. Although
two from Ontario (Mulligan 1975), and two from recent authors have said little regarding itsprobable
Saskatchewan (Mulligan 1966, 1975). It appears relationships, Hitchcock (1941) states that its clos-
that my determination ofn = S (Table 1) fromDag- est relative is D. oreibata J. F. Macbr. & Payson, a
gett Co., UT is the first report forthe United States. species under which it was subsumedpriorto 1932.
None ofthe previous North American reports spec- The latter taxon is endemic to central Idaho in its
ify variety, though most are surely var. nemorosa, typical form, is similarly white-flowered, and
the taxon to which my count is assigned following shows a chromosome number of n = 16 (Hender-
the taxonomy of Kartesz (1994). Although the gla- son et al. 1980). In light of its proposed relation-
brous-fruited form (var. leiocarpa) is considered ships and the assumption that D. subalpina was a
taxonomically insignificant by many authors, there member of the white-flowered euploid group, the
does appear to be some geographic integrity to its actual chromosome number was unexpected. Based
occurrence. Therefore, it seems wise to maintain on at least ten cells from five individuals in each
the distinction until North American populations of three populations, the chromosome count of
are studied adequately. Draba subalpina proves to be « = 13 (Table 1).
Although Hitchcock (1941) considersDraba rec- Whether D. subalpina belongs to a relatively rare,
tifructa to be a close relative of euploid D. nemo- white-flowered aneuploid group or is more closely
rosa, little evidence is cited to support such an as- related to some of its yellow-flowered congeners
sociation. Instead, it appears to be very closely re- remains to be deternuned. The close proximity (ca.
lated to D. albertina, distinguished from that spe- 60 km) of D. sobolifera, the only other species
cies mainly by its pubescent upper stems and known to exhibit « = 13, raises intriguing possi-
pedicels. Ongoing studies of populations in north- bilities regarding the relationships of white- and
em Utah suggest that D. rectifructa and D. alber- yellow-flowered aneuploids in Draba.
tina hybridize when growing in close proximity. Even with the small sample size of this nascent
Thus, it is not surprising to find that D. rectifructa effort, it is clear that the taxonomic composition of
has a chromosome number of n = 12 (Table 1), the Intermountain Draba flora is quite different
identical to that of its putative aneuploid relative. from the intensively studied assemblage of Canada
Draba sobolifera, endemic to the Tushar Moun- and Alaska. In the latter. Mulligan (1976) assigned
tains of southern Utah, is considered a member of 17 species to his white-flowered euploid group,
Hitchcock's (1941) ventosa group with close affin- nine to the yellow-flowered euploid assemblage,
ities to D. cusickii Robinson & D. E. Schulz (Rol- and 13 to his yellow-flowered aneuploid group. In
lins 1993). The chromosome number of the latter my sample from Utah, Wyoming, and Arizona,
species is unknown, but the two members of the white-flowered euploids are not represented (unless
ventosa complex previously reported, D. ventosa D. cuneifolia belongs here) and yellow-flowered
and D. ruaxes, show 2n = 36 and 2n = 72 (Mul- euploids arerare, comprising onlyD. nemorosa and
ligan 1971). They are considered to be triploid and possibly D. maguirei. Seven of the Intermountain
hexaploid respectively, with a base number ofx = taxa belong to the yellow-flowered aneuploid as-
12. Cytological studies on a population of D. so- semblage and the remaining taxon {D. subalpina)
bolifera from Piute Co., UT reveal that it is a sex- is a white-flowered aneuploid of uncertain affinity.
ually-reproducing taxon with a chromosome num- A growing number of chromosome counts for
ber of n = 13. This is the last number to be doc- the region suggests that the Intermountain West
umented in Mulligan's (1966, 1976) aneuploid se- may be a center of diversity for aneuploid Draba.
ries, and it firmly establishes this species as a With the discovery of both n = W and /i = 13
member of the yellow-flowered aneuploid group. among local endenaics, a complete series of base
There are three previous chromosome counts for numbers extending from 8 to 16 has been docu-
Draba spectabilis, all from Colorado and all as- mented. Only n = 9 and « = 14 are missing from
signed to var. oxyloba (Greene) Gilg. & O. E. my sample, and those numbers have been con-
Schulz by Price (1980). The earhest report (Mulh- firmed in other taxa from the region. This means
gan 1966) of n = 10 seemed to indicate that the that every major step in the process of aneuploid
species belonged in the aneuploid group. However, evolution is preserved among the Draba species of
two subsequent counts of n = 16 and n = 16 ± 2 the Intermountain West. In this assemblage ofDra-
by Price (1980) suggest an affinity to the yellow- ba species, we have an unprecedented opportunity
flowered euploid assemblage. My determinations, to study the processes of chromosomal evolution
apparently the first forvar. spectabilis, are fromtwo and speciation in plants. With further cytological
widely separated populations in San Juan Co., UT sampling and concurrent DNA studies ofthe group,
(Fig. 6). They agree with Mulligan's (1966) report we soon may be in a position to elucidate the evo-
2000] WINDHAM: CHROMOSOME COUNTS ON DRABA 11
lutionary history of this interesting and diverse set Love (ed.), lOPB Chromosome Number Reports
of organisms. LXVIII. Taxon 29:534.
Holmgren, P. K., N. H. Holmgren and L. C. Barnett.
Acknowledgments o(efdst.h)e. 1W9o9r0l.d,In8dtehxeHde.rbNaeriworYuomr.kPaBrottaI:niTchaelHGearrbdaerni,a
NatIurwailshHitsoteoxrpyre(sUsMmNyH)graatnidtutdheetsotatfhfeoUftWaahsaMtucshe-Cuamchoef KarteBsrozn,xJ,. TN.Y.1994. A SynonymizedChecklistoftheVas-
National Forest (especially Wayne Padgett) for providing cular Flora ofthe United States, Canada, and Green-
funding that made this work possible. Thejob oflocating land, 2nd ed. Timber Press, Portland, OR.
the rarer taxa and estimating the dates of meiosis was LiCHVAR, R. W. 1983. Evaluation of Draba oligosperma,
D. pectinipila, and D. juniperina complex (Crucifer-
greatly facilitated by access to the extensive collectionsof
tiShnpteeecrSie.asltL.tihnWaenDlkrssahbaraHeeadrnubdearRwi.huomDsoe(uBghrleialgsphSaatmnodnYeo,duewndihgcoaUtnpiiiovqneurestdoitmyt)hy.e Love,a(ee)dA..)..GralenaOdtPBBDa.sCiLhnorvoNeam.tousr1ao9l8mi2se.tN4Pp3u.:m4b41e12r-04-4R14e2p.6oritnsAL.XXLIoVv.e
Taxon 31:119-128.
pa(rEoxmjhaeijcbotirt(safnaDdcetpoaarbritliimnteynitttso,sfUuicnMcdeNsbHsu.d)sIfuaonlrsdoheertlghpoaiwnnikgthEmretiihnoesiKfsii)ngucwraeaissd, Moorneu,mbRe.rsJ.fo(red.1)9.671-91793.71.IndReexgntuomplVaengtetcahbriloemo9s0o:m1e-
539.
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