ecogeographic races of lesquerella engelmannii (cruciferae): distribution, chromosome numbers, and...

ECOGEOGRAPHIC RACES OF LESQUERELLA ENGELMANNII (CRUCIFERAE) : DISTRIBUTION, CHROMOSOME

NUMBERS, AND TAXONOMY 1

CURTIS CLARK 2

Abstract. Morphological, karyological, and ecological data indicate that Lesquerella engelmannii (Gray) Wats. should be considered with L. ovali]olia Rydb. as comprising a single polymorphic species having diploid, tetraploid, hexa- ploid, and octaploid populations and exhibiting broad variation, with geographic trends, in vegetative morphology. Three subspecies are distinguished.

Lesquerella engelmannii (Gray) Wats. and Lesquerella o vali/olia Rydb. are two petrophilous perennials from the southern plains of the United States. Close affinities between the taxa have been noted by Payson (1921) and Rollins and Shaw (1973) and implied by Rydberg (1917). Coulter and Nelson (1909) united the taxa at the specific level. Segregated or united, the species are highly variable with respect to morphology, karyology, and soil preference. Rollins and Shaw (1973) recognized much of this variation; however, additional collections and chromosome numbers reported here necessitate a reevaluation of the taxonomic grouping and indicate that the species should be united.

MATERIALS AND METHODS

Investigations began in March, 1972, and were terminated in April, 1974. Plants were collected throughout the southern two-thirds of the range of the group, material for chromosome counts was obtained from 45 populations, and a study of reproductive biology was carried out at the following eight populations:

A R P K - Oklahoma. Murray Co.: Arbuckle Peak, a rounded hill off OK Hwy 77d in the Arbuckle Mountains, W edge of Sec 29, T1S, R2E. Viola limestone.

JP - - Oklahoma. McClain Co.: Johnson's Pasture Grassland Research Plot, on OK Hwy 9, 4.1 mi. W of junction with Interstate 35. Duncan sandstone.

LCC - - Oklahoma. Johnston Co.: Lone Cedar Cemetery, E of Baum, W half of Sec 31, T3S, R4E. Baum limestone.

LL - - Oklahoma. Comanche Co.: Lost Lake road, 0.6 mi. S of junction with OK Hwy 49, in Wichita Mountain Wildlife Refuge. Granite.

MAR - - Oklahoma. Stephens Co.: S of Marlow, on US Hwy 81, 0.7 mi. N of junction with OK Hwy 7 westbound, E edge of Sec 31, T2N, RTW. Duncan sandstone.

PF - - Oklahoma. Grady Co.: Polygala Flats, on OK Hwy 9, 2.7 mi. E of Tabler, SE corner of Sec 24, T7N, R6W. Sandstone.

PI-I - - Oklahoma. Stephens Co.: Petticoat Hill, 5.2 mi. E of junction with US Hwy 81 on Bois D'Arc Rd (old OK Hwy 7), between Sec 6, T1S, R6W, and Sec 1, T1S, RTW. Duncan sandstone.

TAB - - Oklahoma. Grady Co.: 1.9 mi. E of Tabler on OK Hwy 39, NW corner of Sec 36, TTN, R6W. Sandstone.

Chromosome Counts.--Buds were fixed in chloroform, 95% ethanol, and glacial acetic acid (6:3:1 v /v /v ) for 24 hours. The material was washed and stored in

1 This research was carried out in partial fulfillment of the requirements for the Master of Science degree from the University of Oklahoma. Support was provided by a grant from the Oklahoma Biological Survey and by a National Science Foundation Graduate Fellowship. I thank Karen W. Bowers, James R. Estes, George J. Goodman, Phillip M. Hall, Ethen Perkins, Paul G. Risser, Gary D. Schnell, Ronald Segal, Robbin W. Thorp, John and Eve Williams, Joseph T. Yacovino, and my wife Barbara for their assistance.

2 Department of Botany, University of California, Davis, CA 95616.

BRITTONIA 27: 263--278. July-September, 1975.

263

264 BRITTONIA [VOL. 2 7

70% ethanol at room temperature. Buds were bulk stained at room temperature in HCl-alcohol-carmine (Snow, 1963) for four days, washed in 70% ethanol, and dis- sected in 70% ethanol or 45% acetic acid. Anthers were mounted in Hoyer 's medium (Alexopoulos & Beneke, 1952); squashes were viewed with bright-field optics. Chromosome numbers were determined in the microspore mother cells at meiosis or during the mitoses of the microspore. Drawings were made with a camera lucida.

Cultivation and Transplantation.--Seeds from JP and LCC were germinated under greenhouse conditions in sand, potting soil (1 loam : 1 sand : 1 peat), and soil from JP, LCC, and LL, and in the laboratory on perlite, flint shot, and filter paper.

Plants were transplanted from LCC to JP and from JP to LCC on 15 April 1972; one plant at each locality survived and flowered the following spring. Transplants involving plants at ARPK, MAR, and PH, carried out during the spring of 1973, were unsuccessful, as were transplants from the field to the greenhouse.

Reproductive Biology.~nsect-exclusion cones ca. 0.5 m tall and made of 14-mesh window screen, and parchment paper pollination bags were set out at ARPK and PF; cones covered one to several plants and bags covered a single inflorescence.

Flowers were photographed with Tri-X film and an 18A filter, which transmits near-ultraviolet but excludes other wavelengths. Dried material was observed with a chromatography viewer using a 336 nm light source. To determine the age of plants I counted successive groups of flowering stem bases on the caudex (assuming one group per year), or, when these were lacking, successive groups of basal leaf bases. The number of seeds per plant was estimated on the basis of 10 seeds/silique, 10 siliques/infructescence, and 5-10 infructescences/plant; the figures are approxi- mations, based on counts from about 20 plants. Seed weight was determined as the average of 25 seeds.

Morphological Characters.--I determined the abundance and distribution of U- notched trichomes on the basis of my collections, finding the percentage of plants at a site having at least five clearly U-notched trichomes in a 3.2 mm diameter circle (the 50>< field of the microscope used) taken near the center of the blade of one of the larger basal leaves. The variation in the broadness of basal leaves was assessed by determining the ratio of length (including petiole) to width of one of the broader basal leaves of each plant examined for trichome character.

Collections and Vouchers.--Herbarium specimens were borrowed from cs, GH, KANU, KSC, MO, NY, SMU, Southwestern State College at Weatherford, Oklahoma (swsc) , TEX, TTC, and us, and examined at COLO, UNM, OKLA, and RM. Research was carried out in conjunction with the Bebb Herbarium of the University of Okla- homa (OKL), where vouchers of chromosome counts and other plant collections are deposited.

Insect pollinators were collected at ARPK, LCC, MAR, PH, TAB, PF, and JP. Vouchers are deposited with a collection of insect pollinators at the Department of Botany and Microbiology, University of Oklahoma.

TAXONOMY AND DISTRIBUTION

LESQUERELLA ENGELMANNII (Gray) Wats. (Synonymies and typifications are given under subspecific headings.) (Fig. 2)

Plants perennial, leaves and stems moderately to densely pubescent; trichomes stellate, the rays (3) 6-25 (30), symmetrically disposed, or asymmetrically, forming

1975] CLARK: LESQUERELLA ENGELMANNII 265

Fro. 1. Trichome shape in Lesquerella engelmannii. Left, U-notched trichomes (arrows) ; right, symmetrical trichomes.

a U-shaped notch (Fig. 1), bases free or fused; taproots woody, simple or branched, to 50 cm long and more; caudices woody, simple to elaborately branched, slender to enlarged, ascending to decumbent or rarely stoloniferous, 0.5-11 cm long (up to 17 cm in erect and 22 cm in stolon) ; basal leaves 0.5-9 cm long and 0.3-2.5 cm wide, the blades lanceolate to elliptic to oval, obovate, deltate, lyrate, or orbicular, merging gradually to abruptly with the winged petiole, margins entire to remotely dentate or sinuate, leaves broadening with age and turning purple or gray in senescence; fruiting stems ascending, 5-40(76) cm tall, few to several from each caudex branch; cauline leaves 0.5-4 cm long, 2-6 mm wide, entire, elliptic, sessile or short-petiolate; in- florescences dense, buds ellipsoid; sepals pubescent, at anthesis 4-7 mm long; petals 7-14 mm long, white or yellow, the white ones yellowing upon drying, the yellow ones fading, the region of the midvein reflecting near-ultraviolet for the proximal half of its length, fluorescing yellow in long-wave ultraviolet upon drying; paired stamens 6-11 mm long, single stamens 4-8 mm long; pollen elliptical to orbicular, often both pentacolpate and hexacolpate in the same anther; infructescences dense, subcorymbose to racemose and occasionally elongated; pedicels 4-20 mm long, straight or curved, horizontal to ascending but usually divaricate; siliques (1) 3-17 (28) per infructescence, (2.5)4-7(9) mm long, sessile or short stipitate, globose to elipsoid, the valves glabrous on exterior and interior; styles 3.5-9 mm long, persisting; septum entire, ovules 2-8 per locule, seeds about 2 mm long, flattened, orbicular, orange-brown to dark brown, neither margined nor winged, upon imbibement surrounded by a clear gelatinous layer to 1 mm thick; cotyledons of the seedling suborbicular to obovate, glabrous, borne above the soil surface.

Lesquerella engelmannii is a highly polymorphic species occurring sporadically and in populations of many hundreds of individuals in the southern plains of the United States. I t is restricted primarily to xeric rather well drained soils, most often on rocky outcrops and hillsides. I t grows in close association with the parent material, which may be sandstone, limestone, or granite, or less commonly certain shales and anorthosite. I t is generally found in areas of sparse vegetation but also occasionally in prairies, oak and juniper savannahs, and on the rocky banks of watercourses.

Flowering is in March, April, and May, and the species is apparently xenogamous and entomophilous, the pollen vectors being butterflies, bees, and flies (see treatments of each subspecies). The UV-reflecting region along the lower half of the petal midvein may serve as a nectar guide, causing the claws, which surround the stamens, pistil, and nectaries, to contrast in an insect's vision with the blades. This pattern is found in several genera of the Cruciferae (Horovitz & Cohen, 1972).

The plants produce roughly 500-1000 seeds per plant each year, and occasionally as many as 5000 seeds per plant. Seed dispersal seems to be limited. The siliques dehisce while attached to the plant, releasing the seeds, which weigh about 1.3 mg each.

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FIG. 2. Distribution of Lesquerella engelmanniL

The seeds are denser than water but can be supported by surface tension; water transport would usually carry them downhill into lowlands of generally unsuitable habitat. Wind transport is possible, but the seeds are too small and dense to be very buoyant. Many seeds germinate in the vicinity of the parent plant, seedlings beginning to appear in the early summer following fruit dehiscence; some seeds overwinter and germinate early the following spring.

Ages of 10 to 12 years are not uncommon among plants in the northern parts of the range, and Stephens 31319 (Nu and 47875 (OKL) probably exceed 20 years. The plants seem not to flower before their second year (Cory 55802, sMu, the youngest flowering individual examined).

Plants seldom survive transplantation in the field during the flowering season; of over a dozen transplants to the greenhouse, none survived. Seeds germinate easily


on a number of different soils, sand, and even on Whatman filter paper, but the plants are not hardy in cultivation and seldom flower, the flowers produced being malformed.

The species consists of three groups, treated here as subspecies. They differ in morphology, soil preference, and range of chromosome numbers, and each is geo- graphically discrete.

KEY TO THE SUBSPECIES OF LESQUERELLA ENGELMANNII

1. Flowers white; caudices simple or few-branched; plants of limestone, granitic, and anorthositic soils in the Wichita and Arbuckle Mounta ins and adjoining regions of Oklahoma, and of rare occurrence on soils of the Stanley shale in the Ouachita Mounta ins of southeast Oklahoma ............................................................................ 2. L. ENGEL2ClANNII SSP. ALBA

1. Flowers yellow, or if white, plants of north-central Kansas ; caudices sometimes simple bu t usually many-b ranched ; plants not of the Wichita, Arbuckle, or Ouachita Mountains , or if of these regions, plants of rocky red sandstone soils. 2. Tr ichomes generally symmetr ical (Fig. 1); basal rosettes well developed; caudices

generally compact ; plants of rocky red sandstone soils in central and south-central Oklahoma, and of the caprock, river bluffs, and breaks in the plains f rom the Texas panhandle nor th to Colorado, Kansas, and Nebraska . . . . . . 3. L. ENGELMANNII SSP. OVALIFOLIA

2. Trichomes most ly U-notched (Fig. 1); basal rosettes not well developed; caudices often elongate; plants of limestone soils in north-central Texas and along the Balcones Escarpment in south-central Texas .................................... 1. L. ENGEL:IVIANNII SSP. ENGELMANNII

1. LESQUERELLA ENGELMANNII SSP. ENGELMANNII

Vesicaria engelmannii Gray, Gen. F1. Amer. Bor.-Orient. Illus. 1: 162. 1848. Type: TEXAS. Pebbly shores of the Guadaloupe, New Braunfels, May 1846, Lindheimer 325 (Holotype, GH; isotypes, MO!, OH, B, K).

Vesicaria pulchella Kunth & Bouch6, Ann. Sci. Nat. Bot., s6r. 3 2: 229. 1849. Type: Grown from seed (Rollins & Shaw, 1973) (Holotype, B).

Vesicaria engelmannii var. fl elatior Gray, Boston J. Nat. Hist. 6: 145. 1850. Type: TEXAS. Pebbly river banks, New Braunfels, May 1848, Lindheimer 576 (Holotype, GI-I; isotypes, Mo!, K, UC).

Lesquerella engelmannii (Gray) Wats., Proc. Amer. Acad. Arts 23 : 254. 1888. Alyssum engelmannii (Gray) Kuntze, Rev. Gen. P1.2: 931. 1891.

Distinguishing characters given in the key. Chromosome numbers: n = 6, 12, 18 (Appendix 1; Figs. 3, 4).

Plants of subspecies engelmannii are found in Texas on limestone soils in a band from Montague and Collin counties south to Burnet County and along the Balcones Escarpment from Travis County as far south as Bandera County. The plants are common in the northern part of the range on gravelly hillsides; populations are infrequent on the hills of massive porous limestone of the Escarpment. The type collection, several other Lindheimer collections from New Braunfels, Rollins 5366 (Mo) from Guadalupe County, and perhaps McCaskill s.n. (TEX) from Caldwell County were collected on the pebbly banks of rivers flowing from the Escarpment.

Correll & Correll 29500 (OKLA) from Montague County, west of Forestburg, is cited by Rollins and Shaw (1973) as L. ovali/olia. Clark 422 (OKL), collected at the same or a nearby site, grows on the same limestone and has the same chromosome number (n -- 18) as subspecies engelmannii of that region. Although both collections have oval basal leaves, it seems most reasonable to assign them to subspecies engelmannii.

The morphology of subspecies engelmannii is quite variable. Some plants have simple caudices, whereas most are extensively branched. Trichomes of subspecies engelmannii are generally U-notched (Figs. 1, 6; Table 1 ) although less so among the northern populations. The number of rays per trichome is variable.


FIG. 3. Distribution of chromosome numbers, based on my counts and those of Rollins and Shaw (1973).

Payson (1921 ) separated L. ovali]olia from L. engelmannii on the basis of the basal leaves, those of L. engelmannii being narrowly oblanceolate and those of L. ovali- ]olia ovate. In herbarium collections of subspecies engelmannii, most of which were made toward the end of the flowering season, the basal leaves are indeed oblanceolate. In early spring collections, older basal leaves still remain on the plant, and these are most often oval or obovate; in Clark 433 (OKL) they are among the broadest in the entire species. The margins of these leaves are often sinuate.

The sterile shoot described by Payson (1921) and Rollins and Shaw (1973) corresponds in part to the elevated caudex of Rollins and Shaw (1973). I t is formed as a single season's elongation of the caudex, is sterile the first year or two, and forms flowering stems during subsequent years. I have seen no sterile shoot with leaves from more than one or two years of growth. Shoots in flower are evident on Shinners 12179 (SMU), Lundell 13474 (EL, us), Tharp s.n. (TEX), and Johnson 467 (TEX). This growth pattern is most common in the southern parts of the range of subspecies engelmannii, but it is even found in subspecies ovali]olia as far north as central Okla- homa. In general, branching is more open and more growth occurs each year in the southern populations of the subspecies.

There seems to be little correlation between morphology and chromosome number. In a single population in Lampasas County (Clark 433, OKL, n = 18), one spreading plant in a roadside depression exceeded 15 cm wide, with the large basal leaves described above, whereas other plants on a denuded limestone mound no more than a meter away were small, stunted, and bore a great resemblance to subspecies ovali- ]olia of the southern Texas panhandle. Yet Clark 426 (OKL, n = 18) and 427 (OKL,

1975] CLARK: LESQUERELLA ENGEL1V[ANNII 269

434 432

427

412

129

116 439a 438a

439b 438b

317

273

O. 0 1 n n m

4 4 0

FIG. 4. Camera lucida drawings of chromosome figures. Lesquerella engelmannii ssp. engel- rnannii: 434, microspore mitosis; 427, diakinesis; 432, microspore mitosis. Lesquerella engeImannii ssp. alba: 129, microspore mitosis. Lesquerella engelmannii ssp. ovali]olia: 412, anaphase I; 116, microspore mitosis; 439a, polar anaphase I, both sides n ~_~ 18; 438a, microspore mitosis, n ~--- 19; 439b, microspore mitosis, n = 20; 438b, microspore mitosis, n ~-~ 23; 273, diakinesis, n ~ 24 (material faded before drawing was made; only 23 pairs discernable) ; 317, microspore mitosis, n 25 ; 440, microspore mitosis, n ~ 26.

n ---- 12), g rowing wi th in a mile of each o ther in H a y s County , are morphologica l ly indis t inguishable .

P lan t s of subspecies engelmannii flower f rom m i d - M a r c h to ear ly M a y ; in general , p lants wi th n = 12 f lower la ter than those wi th n -- 6 or n = 18. But te r f l ies and bees were observed v is i t ing p lants in Pa rke r County .


2. Lesque re l l a e n g e l m a n n i i ssp. a lba (Goodman) C. Clark, comb. nov.

Lesquerella ovalifolia Rydb. var. alba Goodman, Rhodora 38 : 239. 1936. Type: O~=LAHO~A. MURRAY CO.: hilltop, Arbuckle Mts., April 7, 1934, Goodman 2077 (Holotype: OKL!)

Lesquerella ovalifolia ssp. alba (Goodman) Rollins & Shaw, Genus Lesquerella in North America, p. 127, 1973.

Distinguishing characters given in the key. Chromosome numbers: n = 6 (Appendix 1; Figs. 3, 4).

Plants of subspecies alba occur in southern Oklahoma in two regions--an eastern one centered on the Arbuckle uplift and a western one centered on the Wichita Mountains. I t is replaced by subspecies ovalifolia in the area between these regions.

In the east subspecies alba is common on the limestones, limestone-derived con- glomerates, and dolomite of the Arbuckle Mountains in Murray, Carter, Johnston, and Pontotoc counties. I t also occurs on the Har t limestone, a Permian outwash surrounding the northern and western parts of the Arbuckles, in Garvin County (Clark 292, OKL), Carter County, and Murray County; on the Precambrian granite of Johnston County; on the Cretaceous Baum limestone hills along the Washita River in Johnston County, and on the Cretaceous Goodland limestone in Love County (an extension of the limestone strata that support subspecies engelmannii in north central Texas).

I was unable to locate the population of Taylor 1904 ("in open field, 3 miles north of Durant ," Bryan Co., o~:I,) ; the area may have been disturbed by the construction of a new interchange for U.S. Hwy. 75. Subspecies alba is found in Pushmataha County on the banks of Rock Creek near Rattan (Waterfall 15255, us, OKL, O~:LA: Clark 136, 199, OKL) in gravel of the Stanley shale. D. Edwards s.n. ("Fort Towson Ark.," ~n) can probably be referred to this population. Fort Towson was near Hugo in Choctaw County, Oklahoma, about 15 miles from the Rattan site.

The locations of Waterfall 9346 (KANU, OI(LA, SMU) and 8834 (OKL, OKLA) are within a half mile of each other southeast of Smithville in McCurtain County, on the Stanley shale. I was unable to find plants of the subspecies in this area.

In the west, populations of subspecies cdba are common on the granite of the Wichita Mountains of Comanche and Kiowa counties, although they have not been reported from the gabbro of this region. There is an occurrence on anorthosite south of Roosevelt in Kiowa County (Buttmm 7, OKL; Clark 264, OKL). Plants of the subspecies are also found on the limestone hills north of the Wichitas in Kiowa and Caddo counties and on the Postoak conglomerate, a Permian outwash from the Wichitas.

There is an isolated group of collections from Washita County (Watts 42, swsc) and Custer County (Sylvester 123, swsc; Clark 307, OKL), in the region of the Weatherford gypsum. Examination of the parent material at Clark 307, however, showed it to be limestone.

I have referred McClellan 67 (OKL) from McClain County, cited by Rollins and Shaw (1973), to subspecies ovali/olia. I t is an unusual collection, the plants appear- ing to have flowered in their second or third year, and having been collected in fruit. The dirt remaining on the roots of these plants indicates that they grew in the same red sandstone that supports the many yellow-flowered plants of that region.

The caudices of subspecies alba are commonly unbranched, being occasionally branched in the western part of the range, but never so elaborately as either of the other two subspecies. The caudices are often quite thick, sometimes exceeding 1 cm in diameter with old leaf bases still attached. The basal leaves are variable (Table


1; Fig. 5), ranging from lanceolate to deltate, oval, obovate, and lyrate, and are often sinuate-margined, especially in mesic localities. In some plants the older leaves are lost when quite small; in others they reach considerable size. U-notched trichomes (Figs. 1, 6; Table 1) are not common in the subspecies.

The transplant from LCC at jP set fruit, but the seeds were poorly formed and did not germinate. This indicates 1) that the transplant was visited by insects, since plants in insect exclusion cones at ARPK did not form fruit, and 2) that the transplant was neither apomictic, autogamous, or geitonogamous, viable seed being expected in these cases. Thus the transplant appears to be xenogamous, and incapable of crossing with plants at JP to produce viable seed (plants at JP are n = 12).

There was not fruit set in 10 pollination bags at ARPK; this is in accordance with the conclusions drawn from the transplant experiment.

Insect visitors are summarized in Appendix 2. Only one of the Apis collected at LCC carried a pollen load.

3. Lesquere l la e n g e l m a n n i ssp. oval i fol ia (Rydb.) C. Clark, comb. nov.

Lesquerella ovali/olia Rydb., Britton & Brown, Illustr. F1. 2: 137. 1897. Type. NEBRASKA. KIMBALL CO.: Hills of upper Lawrence Fork, 11 Aug 1891, Rydberg 22 (Holotype, Nu isotypes, NY!, us) .

LesquereUa ovata Greene, Pittonia 4 : 308. 1901. Type. COLORADO. Bluffs at Pueblo, June 1873, Greene s.n. (Lectotype, Rollins & Shaw, 1973: ND-G; iso- lectotype, F; syntype, Mo ! )

Distinguishing characters given in the key. Chromosome numbers: n = 6, 12, 18, 19, 20, 23, 24, 25, 28 (Appendix 1; Figs. 3, 4).

Plants of subspecies ovali]olia are found in central and south-central Oklahoma and in a broad region from south of the Texas panhandle north into Colorado and Kansas.

In central Oklahoma the subspecies occurs in Stephens, Grady, Garvin, McClain, and Cleveland counties on the Duncan sandstone, a rather resistant red Permian stratum that dips to the north and west, rising to a low line of hills on its southern and eastern sides. A single population (Clark 282, OKL) has been found on a road cut in the Garber sandstone about a half mile from the Stephens County Line in Carter County, and populations are also found along the bluffs of the Washita River in Grady County.

In the western region, subspecies ovalifolia inhabits the edge of the Tertiary caprock and the nearby eroded redbeds in the Texas panhandle as far south as Scurry and Gaines counties and in northwestern Oklahoma as far southeast as Roger Mills County; the basaltic Mesa de Maya in southeastern Colorado and Cimmaron County, Oklahoma; the bluffs of the Red and Canadian rivers in Texas and New Mexico, the northern Pecos River in New Mexico, the Cimmaron River in Kansas and Oklahoma, and the Arkansas River in Kansas and as far west as Fremont County, Colorado; and breaks in the plains as far north as Rooks County, Kansas. Plants are found grow- ing on sandstone, sandy limestone, basalt and occasionally loose broken shales.

The type locality in Kimball County, Nebraska, is about 200 miles removed from the nearest collections to the south; there have been no Nebraska collections since (Winter 1936; Rollins & Shaw, 1973 ). I t is possible that Rydberg made a labeling error, but the Lawrence Fork dips into Kimball County only a short distance; most of its length is in Banner County. Thus some care must have been exercised in establishing the location. The area between the type collection and the nearest collections to the south has not been well collected, but then neither have the areas of western Kansas and southeastern Colorado where subspecies ovali/olia occurs.


FIGS. 5-6. Basal leaves, length/width. 6. Percentage of plants with U-notched and symmetrical trichomes. (Both maps based on my collections.)

I concur with Rollins and Shaw (1973) that Perkins s . n . (OKLA) from Uvalde County, Texas, represents a labeling error. At the locality cited, 5 miles south of Uvalde, the rocky limestone roadsides support a population of L. argyraea, a perennial species that might be confused with subspecies ovali]olia in the haste of preparing labels for a number of specimens.

Hudson 308 (OKL) from "open pasture by roadside," Hughes County, Oklahoma, may also be a labeling error. An examination of a dozen rocky pastures throughout Hughes County failed to disclose the population, and the red dirt clinging to the roots suggests that it was collected in the red sandstone of McClain or Grady County, Oklahoma.

Jells s.n. (O•L) is labeled "North of Altus, Oklahoma," and annotated "Jackson Co." North of Altus in Jackson County is a region of deep clay soils unsuitable for subspecies ovali]olia. Farther north in Greer and Kiowa counties are granite hills, extensions of the Wichita Mountains. Subspecies alba would be expected here, but I was unable to locate the plants. The collection in question has white or faded yellow flowers and a branched caudex.

Stephens 46796 (~ANU, OKL, Nu from Osborne County, Kansas, has white flowers, and was collected in rocky limestone soil. Stephens (pers. comm., 1974) said that it was abundant on a single hillside but not seen elsewhere, and that he saw no yellow-flowered plants nearby. Stephens 48186 (KANU, OKL, NY) iS from the same location, and the location of Neher 236 (KSC) corresponds with the location of the Stephens collections; both are in fruit. The collections include plants with both branched and unbranched caudices, but none are so thick as those of subspecies alba in Oklahoma. I t seems unreasonable to consider this population to be of the same derivation as the Oklahoma populations of subspecies alba; more likely it arose independently, from yellow-flowered Kansas plants. As it is distinctive from sub-

1975 ] CLARK: LESQUERELLA ENGELMANNII 273

species ovali]olia in Kansas only by its flowers, I have chosen here to refer it to that subspecies.

Caudices of subspecies ovali]olia are often simple in south-central Oklahoma; in the western region most are branched. Branching may be very elaborate, dozens of stems radiating from the base and forming a hemispherical plant a number of centi- meters wide, as in Hitchcock s.n. (Mo 1923470) from Hamilton County, Kansas.

The basal leaves of subspecies ovali]olia are commonly oval or obovate, and vary from lanceolate in the southern Oklahoma populations to orbicular (Table 1 ; Fig. 5). Leaves are generally smaller in the north and west and thus appear more densely pubescent, although the number of trichomes may be no greater than that of larger leaves. Trichomes are only occasionally U-notched (Figs. 1, 6 ; Table I) .

Plants from southern Oklahoma strongly resemble subspecies engdmannii from northern Texas; the trichome character does not always serve to distinguish them, and they can be separated with confidence only by locality and soil preference.

The range of chromosome numbers in subspecies ovali]olia is perhaps the greatest in the genus (Rollins & Shaw, 1973). The predominant level in central Oklahoma is n = 6, a few northern populations being n = 12. Populations of n = 6 are also found in New Mexico and south of the Texas panhandle. The few counts from the region north of these suggest that hexaploids (n = 18), octaploids (n = 24), and perhaps decaploids (n = 30) or dodecaploids (n = 36) have arisen and hybridized. Meiotic irregularities in the higher levels and hybrids resulting in nonpaired chromosomes lead to unequal distribution of chromosomes, resulting in anthers containing microspores with several chromosome numbers. Pollen fertility at these levels suggest that fertility of the hybrids is not impaired.

Subspecies ovali]olia flowers from late March to late May, flowering later in the northern parts of the range.

The transplant from JP at LCC set fruit; the seeds were poorly developed and did not germinate. In addition, no fruit was set in either the pollination bags or the insect exclusion cones at PF. Xenogamy can be inferred, as it was for subspecies alba, and in this case also the transplant was of a different chromosome level than the native plants. Insect visitors are summarized in Appendix 2.

Discussion

Taxonomy.--Coulter and Nelson's (1909) placement of L. ovali]olia in synonymy with L. engelmannii is surprising, since at that time there were almost no collections from the intervening Oklahoma populations. Collections from Colorado differ con- siderably from the early south Texas collections of L. engelmannii, being shorter and more compact, with smaller flowers and generally broader basal leaves. (Their concept of the limits of the species might be questioned, since they also tentatively included L. pruinosa in it. This was probably based on Greene's (1901) description since later Rollins and Shaw (1973) saw only six collections. Lesquerella pruinosa is quite distinct from either L. ovali]olia or L. engelmannii, but the description does not adequately convey the differences.)

Other authors have had differing opinions of the line separating L. ovali]olia and L. engelmannii. Rydberg (1917) reported both species from Colorado and New Mexico, the former differing from the latter by its smaller size. Payson (1921) included in L. engelmannii not only the central Texas populations but also a collection from Ellis County, Oklahoma. With the material available to Rollins and Shaw (1973), they still chose to include a collection from north-central Texas in L. ovali]olia. All previous authors noted that the taxa were related and made efforts to distinguish them.


TABLE 1. Variation in U-notched trichomes and basal leaves in L. engelmannii. The data for U-notched trichomes are the percentages of plants in the sample having at least five U-notched trichomes per disc 3.2 mm in diameter near the center of the blade.

Collection Sample Percent with Basal leaf number size U-notched trichomes length/width

L. ENGELI'CI~ANN'II SSP. ENC.EL~VIANNII

288 12 92 6.0 289 12 83 6.3 421 8 75 3.2 422 3 100 3.1 423 6 67 3.3 424 4 100 3.0 427 9 100 4.6 428 8 87 4.4 429 6 100 4.8 432 5 IO0 4.7 433 4 75 3.7 434 7 100 3.1 436 7 57 2.5

L. ENGELMANNII SSP. ALBA

113, 258 9 22 2.1 114, 148, 174 14 7 2.9 120 5 0 1.9 123 10 30 3.5 136, 199 20 20 3.0 264 3 67 2.0 283 12 25 3.2 307 10 10 2.6 311 6 17 2.6

L. ENGELMANNII SSP. OVALIFOLIA

92, 94 12 17 1.9 116 7 29 2.2 138 4 25 2.8 237 7 0 2.4 282 7 43 4.0 291 7 86 5.1 295 16 69 4.6 297 6 17 2.7 298 8 37 3.4 303 9 44 3.2 317 15 20 3.0 337 6 17 3.0 344 6 33 3.2 345 6 0 2.9 413 4 50 2.2 437 3 0 2.1 439 7 0 2.6

Thus , f r o m a his tor ical s t a n d p o i n t , the ques t ion is no t so m u c h w h e t h e r the species

should be un i t ed b u t r a the r w h y t h e y were ever sepa ra ted . T h e type col lect ion of

L. ovalifolia u n d e r s t a n d a b l y d i f fe rs cons ide rab ly f rom t h a t of L. engelman~i, since

t h e y were col lected a t the ex t r emes of the range of the group; in add i t ion , the t ype

of L. engelmannii grew on the b a n k s of a r iver, whe reas t h a t of L. ovalifolia grew

on a hil lside. At the t ime t h a t he descr ibed L. ovalifolia, R y d b e r g had seen no

1975 ] CLARK: LESQUERELLA ENGELMANNII 275

TABLE 2. Comparison of presence (-}-) and absence (--) of traits in the three subspecies of L. engelmannii.

eng elmannii ovaIi f olia alba

Yellow flowers + -}- U-Notched trichomes -}- - - Caudex usually branched + + "Sterile shoot" -}- - - Inhabiting sandstone - - -}- n----12 -}- -[- n = 1 8 + + n = 2 4 - - -[-

m

m

m

M

m

collections from Oklahoma, and had only heard reports of collections from Kansas (Britton & Brown, 1897).

There is now additional evidence that the species should be united:

1) Morphological variation is continuous. Those characters used in the past to separate the species undergo a gradual transition with geography. U-notched trichomes are found more commonly in the south; subspecies engelmannii in northern Texas may lack them, and they may be present in subspecies ovalifolia (Figs. 1, 6; Table 1). Basal leaves are generally broader in the north (Fig. 5; Table 1); in subspecies engelmannii the leaves have often begun to senesce before they reach a comparable width. Thus only morphological trends using several characters are useful in distinguishing the taxa.

2) Subspecies alba is as closely allied to subspecies engelmannii as it is to subspecies ovalifolia, associating with each at a similarity of 0.25 (1.0 = identity), using the simple matching coefficient of association (Sokal & Sneath, 1963) with eight characters which together help to separate the taxa (Table 2). Subspecies avaliJolia and subspecies engelmannii show a similarity of 0.50.

3) The absence of viable seed in the two transplant experiments suggests that there may be little gene flow between subspecies, at least when different chromosome levels are involved. However, the same barriers to gene flow would be expected between plants of different chromosome levels within a single subspecies, and in a species so discontinuously and in some places (e.g., Balcones Escarpment; Garvin County, Oklahoma) infrequently distributed, extensive gene flow between populations would not be expected anyway. Rollins and Shaw (1973) maintain that genetic barriers are of less importance to the taxonomy of a group than the changes that take place after the formation of such barriers. Mosquin (1966) and Lewis (1967) suggest that the breeding barrier between polyploids is not in itself a justification for assign- ing specific rank to each chromosome level. Ehrlich and Raven (1969) note that in many cases gene flow may be less important than selection in evolution and speciation.

Evolution.--Much of the variation in vegetative morphology seems to relate to environment; plants in the drier and colder parts of the range tend to be smaller and more compact, regardless of the subspecies to which they belong. Likewise, within a population the plants in wetter microenvironments tend to be more robust. Whether this variation is genetic or a result of phenotypic plasticity is unknown; however, plants in cultivation often develop the sinuate-margined leaves characteristic of plants on moist sites, suggesting the plasticity of this character.


Variat ion in chromosome number cannot be so easily characterized. I t does not correspond to any aspect of habi ta t , nor are the higher levels always at the edges of the range. Mult ivalent formation at the higher levels points to autoploidy. I suspect tha t the pa t te rn encountered is the result of extension of the range by polyploids a n d / o r their replacement of diploids and is subject pr imar i ly to those processes governing seed dispersal and to the selective advantages (if any) of the polyploids.

One might assume that the region of south-central Oklahoma inhabi ted by yellow- flowered plants with n = 6 is the center of origin of the group and tha t polyploids have spread to less favorable areas to the north, west, and south. However, this does not take into account the scarci ty of plants a t the presumed center of origin, the problems of seed dispersal upst ream and against the prevail ing winds, or changes in climate. I t is l ikely tha t the species has assumed its current distr ibution since the Wisconsin glaciation, condit ions during the glaciation being quite unlike those today (Dorf , 1960).

Thus any model to account for the dis tr ibut ion and evolution of the species must take into account the climatic changes since the Wisconsin glaciation, the mechanisms of seed dispersal, the selective advantages of polyploids, and the specific environ- mental requirements of the species. Much of this information is still unavailable.

LITERATURE CITED

Alexopoulos, C. J. & E. S. Beneke 1952. Laboratory Manual for Introductory Mycology. Minneapolis.

Brinon, N. L. & A. Brown 1897. An Illustrated Flora of the Northern United States, Canada, and the British Possessions. Vol. 2. New York.

Coulter, J. M. & A. Nelson 1909. New Manual of Botany of the Central Rocky Mountains (Vascular Plants). New York.

Dorf, E. 1960. Climatic changes of the past and present. Amer. Sci. 48: 341-364. Ehrlleh, P. R. & P. H. Raven 1969. Differentiation of populations. Science 165: 1228-1232. Greene, E . L . 1901. A series of botanical papers: studies in the Cruciferae--IV, 1. New species

of Lesquerella. Pittonia 4: 307-311. Horovitz, A. & Y. Cohen. 1972. Ultraviolet reflectance characteristics in flowers of crucifers.

Amer. J. Bot. 59: 706-713. Lewis, H. 1967. The taxonomic significance of autopolyploidy. Taxon 16: 267-271. Mosquin, T. 1966. Toward a more useful taxonomy for chromosomal races. Brittonia 18: 203-

214. Payson, E. n. 1921. A monograph of the genus Lesquerella. Ann. Missouri Bot. Gard. 8:

103-236. Rollins, R .C . 1966. Chromosome numbers of Cruciferae. Contr. Gray Herb. 197: 43-65.

& E. A. Shaw 1973. The genus Lesquerella (Cruciferae) in North America. Cam- bridge, Mass.

Rydberg, P . A . 1917. Flora of the Rocky Mountains and Adjacent Plains. New York. Snow, R. 1963. Alcoholic hydrochloric acid-carmine as a stain for chromosomes in squash

preparations. Stain Technol. 38: 9-13. Sokal, R. R. & P. H. A. Sneath 1963. Principles of Numerical Taxonomy. San Francisco. Winter, J . M . 1936. An analysis of the flowering plants of Nebraska. Conserv. Dept., Conserv.

& Surv. Div., Univ. Nebraska, Bull. 13


APPENDIX 1

CHROMOSOME COUNTS FOR Lesquerella engelmannii

Lesquerella engelmannii ssp . engelmannii:

288, n ~ 18. TEXAS. WISE CO.: US 380, 1.3 mi. E of junction with US 81 business in Decatur. 289, n ~-~ 12. TEXAS. MON~ACVE CO.: T X 59, 5.7 mi. E of junction with T X 175 in Motnague. 421, n = 18. TEXAS. COOKE CO.: Farm Rd. 2382, 6.4 mi. NE of Saint Jo. 422, n = 18. TEXAS. MONTAGUE CO.: Farm Rd. 1655 0.25 mi. SW of junction of Farm Rd. 455

(Forestburg) . 423, n ~ 18. TEXAS. WISE CO.: Farm Rd. 51, 5.7 mi. N of junction of US 380 in Decatur. 424, n - - 6. TEXAS. COLLm CO.: T X 121, 4.0 mi. SW of junction with Farm Rd. 2862. 425, n ~ 12. TEXAS. HAYS CO.: 5.8 mi. SE of Dripping Springs on Ranch Rd. 12 and Ranch Rd.

150. 426, n ~ 18. TEXAS. HAYS CO.: Ranch Rd. 12, 2.0 mi. S of Wimberley. 427, n ~ 12. T~XAS. BAYS CO.: Ranch Rd. 12, 2.8 mi. S of Wimberley. 428, n --~ 12. TEXAS. TRAVIS CO.: S slope near summit of Mt. Bonnell, N W of Austin. 429, n ~-~ 18. TEXAS. BANDERA CO." Park Rd. 37, 4.9 mi. W of junction wi th Farm Rd. 1283, near

Lake Medina. 431, n ~ 18. TEXAS. BURnEr CO.: US 281, 12 mi. N of junction wi th T X 29 in Burnet. 432, n ~ 18. TLXAS. BUR~mT CO.: US 281, 17.7 mi. N of junction with T X 29 in Burnet. 433, n ~ 18. TwxAs. LAMPASAS CO.: US 281, 7.1 mi. S of Evant . 434, n ~ 6. TEXAs. ERAT T-t" CO.: US 281, 8.8 mi. N of junction with US 377 business, N of Stephen-

ville. 435, n ~ 6. TEXAS. PARKER CO.: Farm Rd. 5, E of Weatherford. 436, n ~ 6. TEXAS. PARKER CO.: Lake Weatherford, bluffs N of dam. 5366,1 n ~ 18. TEXAS. 6UADALUPE CO. (Rollins, 1966).

Lesquerella engelmannii ssp . alba:

113, n ~ 6. OICLAHOMA. LOVE CO.: OK 32, 8.3 mi. W of junction with 1-35, W of Mariet ta. 114, n ~ 6. OKLAHOMA. yOHNSTO~ CO.: Lone Cedar Cemetery, E of Baum. 120, n ~ 6. OKLAHOMA. COMANCHE CO.: OK 115, 0.2 mi. N of junction wi th US 62, N of Cache. 124, n ~ 6. OKLAHOMA. MURRAY CO.: US 77 at Turner Falls overlook. 129, n ~ 6. OKLAttO1VfA. MURRAY CO.: US 177 S of Sulphur. 133, n ~-~ 6. OKLAHOlV~A. JOHNSTON CO.: OK 99, 16.2 mi. S of junction wi th OK 61A, 1.5 mi. N

of junction with OK 7 E-bound. 136, n ~ 6. OKLAHOMA. PIYSHMATA~tA CO.: Rat tan, banks of Rock Creek, 12 mi. E of Antlers. 262, n ~ 6. OKLAHOMA. CADDO CO.: OK 19, 5.0 mi. W of Apache. 264, n ~ 6. OKLAHOMA. KIOWA CO.: US 131, 1.3 mi. S of junction with OK 19 in Roosevelt. 307, n ~--- 6. OKLAHOMA. CUSTER CO.: Access road S side of 1-35, 6.1 mi. W junction wi th OK 54,

W of Weatherford. 53124,1 n ~-~ 6. OKLAHOMA. COMANCHE CO. (Rollins, 1966). 53125, ~ n -~- 6. OKLAHOMA. CADDO CO. (Rollins, 1966).

Lesquerella engelmannii ssp . ovali/olia:

94, n ~ 12. O~AHOMA. McCLAm CO.: OK 9, 4.1 mi. W of junction with 1-35. 116, n ~ 12. OKLAHOMA. GRADY CO.: OK 9, 4.0 mi. E of junction wi th H. E. Bailey Turnpike,

E of Chickasha. 117, n ~ 6. OKLAHOMA. STEPHENS CO.: US 81, 0.7 mi. N of junction wi th OK 7 W-bound. 119, n ~-~ 6. OKLAHOMA. STEPHENS CO.: OK 7 W-bound, 3.2 mi. W of junction wi th US 81. 261, n ~ 6. OKLAHOMA. STEPHENS CO.: Pet t icoat Hill, 5.2 mi. E of Duncan, old OK 7. 273, n ~- 24. OKLAHOMA. ROGER M~LS CO.: OK 33, 9.6 mi. E of junction with US 283, E of

Strong City. 282, n ~- 6. OKLAHOMA. CARTER CO.: OK 7, 0.5 mi. E of Carter-Stephens county line. 290, n ~--- 6. OY~AHOMA. S~PHENS CO.: Duncan Lake. 294, n ~ 6. OKLAHOMA. STEPHENS CO.: OK 29, 1.1 mi. E of junction wi th OK 76 N-bound. 295, n ~ 6. OKLAHOMA. STEPHENS CO.: OK 76 N-bound, 100 m N of junction with OK 29. 296, n ~ 6. OKLAHO!V~A. CARVm CO.: OK 76, 100 m N Garvin-Stephens county line.

1 Collection number of R. C. Rollins (c~) .


317, n ~ 25. OKLAItOMA. HARPER CO.: US 183, 11.7 mi. S of junct ion with US 64 in Buffalo. 412, n ~ 6. OXLA~OZaA. GRADY CO.: OK 19, 9.1 mi. N W of Lindsay, SE of Alex. 413, n ~ 6. OKLAHOMA. GARVm CO.: 3.1 mi. W of Lindsay on OK 19, 0.5 mi. N, 0.6 mi. E, S side

of road. 415, n ~- 6. OKLAhOmA. GARVIN CO.: 1.7 mi. N of Garvin-Stephens line on OK 76, 2.1 mi. W, 3.5

mi. N. 418, n ---- 6. OKLAHOMA. ~cCLAm CO.: OK 76, 16.8 mi. S of junct ion OK 9, 2.2 mi. W ; N of Lindsay. 437, n ---~ 6. TEXAS. CARZA CO.: Fa rm Rd. 669, 3.2 mi. S of junct ion with US 380 in Post. 438, n ~ 18, 19?, 23? Tr.XAS. CROSBY CO." T X 207 at cap rock, S of Caprock. 440, n ~ 24, 26?, 28? TEXAS. BRISCOE CO.: T X 256, 15.6 mi. W of junct ion with T X 70. 7153,1 n ~ 6. NEW MExico. CUADALUPE CO. (Rollins & Shaw, 1973). 7158,1 n ~-~ 18. T~XAS. GRAY CO. (Rollins & Shaw, 1973).

APPENDIX 2

SUMMARY OF INSECT VISITORS TO Lesquerellc~ engelmannii

For the abbreviations of the localities, see Materials and Methods.

Nymphal idae : Vanessa cardui Linnaeus (LCC, PH, JP, TAB) , Euptoieta claudia Cramer (PH, J P ) , Phycoides tharos Drury (ARPK, M A R ) , Asterocampa clyton Boisduval & Leconte (PF) .

Lycaenidae: Strymon melinus Heubner (M AR ) . Hesperidae: Pyrgus communis Grote (MAR, PH, JP) . Pieridae: Colias philodice Latrielle (LCC, PH, JP) . Syrphidae: two species (LCC, AR P K, P H ) . Bombyliidae: one species ( A R P K ) . Apidae: Apis melli]era Linnaeus (ARPK, JP ) . Megachilidae: Osmia sp. ( M A R ) . Halictidae: Halictus ligatus Say ( M A R ) , Dialictus sp. # 1 ( A R P K ) , Dialictus ssp. # 2 and # 3

( M A R ) , Augochlorella striata Provancher (PH) , Agapostemon texanus Cresson (PH) , Euglaeus pectoralis Smith ( M A R ) .

ecogeographic races of lesquerella engelmannii (cruciferae): distribution, chromosome numbers, and...

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