Brewbaker, James L.

Weber, William A.

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PHYSARIA VITULIFERA, A TETRAPLOID SPECIES OF CRUCIFERAEB y  W i l l i a m  A. W e b e r *  a n d  J a m e s  L. B r e w b a k e rTwo species of the genus Physaria, family Cruciferae, are indigenous to Boulder County, Colorado. Physaria australis (Payson) Rollins is limited in its occurrence in the Boulder area to one or two isolated colonies on west-facing outcrops of shales of the Pierre formation a t about 1700 m. altitude about four miles north of Boulder. Elsewhere in Colorado this species occurs most abundantly in the westernmost tier of counties, ranges north and east across the Red Desert of Wyoming, and enters Colorado again on the eastern side of the Rocky Mountains, penetrating as far south as Boulder County. Physaria vitulifera Rydberg is the more abundant species in the Boulder area, found on gravel sand and gravel loam soils of dry, sunny, usually south-facing slopes in the foothill canyons from 1800 m. to about 3000 m. altitude. P. vitulifera is endemic in the area between the Clear Creek and St. Vrain Creek drainages east of the Continental Divide. Both species occupy pioneer habitats. Their geographic ranges and ecological niches do not overlap. P. vitulifera is further isolated from P. australis by its earlier flowering period in comparable situations and altitudes. (See Fig. 1.)Physaria australis and P. vitulifera are morphologically quite distinct. The former has numerous entire, fleshy basal leaves, 2-8 cm. long, with obovate, obtuse blades and broad petioles. The siliques are highly inflated, with shallow basal and apical sinuses, equal above and below, the locules being 6-10 mm. long. P. vitulifera has a few elongate, relatively thin basal leaves, 3-6 cm. long, the margins of which are deeply and broadly incised, oblanceolate to spatulate in outline with narrow petioles. The siliques are not highly inflated but somewhat angular, the sinuses unequal, the apical sinus broad, deep, and open, the locules being 4-8 mm. long (see Fig. 2, A and B).Cytological studies of these species were begun in the spring of 1948. Young flowers of each species were fixed in Carnoy’s fluid and were washed and stored in 70% alcohol. Belling’s iron-aceto-carmine was used for making smears of young anthers. Drawings were made of microspore mother cells undergoing meiotic division, and of mitotic division in the developing pollen grains. The cytological study confirms Rollins’ count (1939) of n =  4 for Physaria australis (see Fig. 3). P. vitulifera was found to be tetraploid with n =  8, the first known occurrence of this condition in the genus. Chromosome counts were made of individuals from several populations in Boulder County; in each instance, the tetraploid number was found*  Assistant Professor of Biology.see Fig. 4). Herbarium specimens documenting the counts are preserved in the University of Colorado Herbarium.According to Rollins, the Colorado physarias fall into two groups of closely re­lated species. P. didymocarpa, P. condensate, and P. australis comprise a primitive group with evolutionary tendencies culminating in P. australis. Only P. australis of this group enters Colorado. P. vitulifera, P. floribunda, P. acutifolia, and P. Oster-PHYSARIA VITULIFERA 25F ig c re  1. Approximate Colorado distribution of the species of Physaria discussed in this paper.P. australis P. vituliferaH B B  P. Osterhoutii p . floribundahoutii comprise a more advanced group. In certain respects P. australis appears to connect the two groups. P. australis, P . floribunda, and P. acutifolia were found by Rollins to have four chromosome pairs.Inasmuch as the tetraploid P. vitulifera and the diploid P. australis now occupy adjacent areas, the origin of the former from the latter or from the la tter’s succes- sional ancestor might be postulated. This hypothesis, however, would imply a similar origin for the other diploid species, to which P. vitulifera is more closelyrelated morphologically. According to Rollins, the closest relatives of P. vitulifera are P. floribunda and P. Osterhoutii; “as a biological entity , the boundaries of P. vitulifera are seemingly well defined; however, recent connections w ith its relatives are strongly indicated.” I t  therefore seems more logical to look to the other mem-PHYSARIA VITULIFERA 27F ig u r e  4. A. Configuration of chromosomes at first meiotic metaphase; Physaria vitulifera Rydberg. X 2900.B. Anaphase chromosomes in developing pollen grain of Physaria vitulifera Rydberg. X  2400.bers of the floribunda group for the origins of P. vitulifera than  to the australis group, with which P. vitulifera bears little morphological relationship.Physaria Osterhoutii Payson m ay reasonably be om itted from consideration a t  the present time. This species, known only from a few collections made a t  Kremm- ling and Sulphur Springs in Grand County, possesses characteristics connecting P. vitulifera, P. floribunda, and P. acutifolia. Rollins m aintained this species withhesitation, since it differs from P. vitulifera by minor features only. Future investi­gation m ay reveal the biological identity  of this form and demonstrate whether or not P. Osterhoutii has played a part in the origin of the tetraploid under discussion.If we accept Rollins’ analysis of morphological relationship, it appears improb­able th a t P. vitulifera arose by autopolyploidy from P. australis. A second pos­sibility is an allopolyploid origin involving P. australis and P. floribunda or proto­types. However, the very close morphological relationship of P. vitulifera to the floribunda group alone makes a third alternative more plausible. The third  pos­sibility is th a t P. floribunda or its successional predecessor once ranged farther north  and east than  it does a t the present time; th a t this population gave rise to an auto tetraploid race on the northeastern periphery of its range; and tha t the te tra­ploid persisted in the area while the diploid was driven subsequently farther south and west. Since no irregularities have been discovered in the meiosis of the te tra ­ploid, it m ay be concluded tha t P. vitulifera, whatever its origin, has now achieved the sta tus of a functional allopolyploid.LITERATURE CITEDR o l l in s , R e e d  C.1939 “The Cruciferous Genus Physaria,” Rhodora 41: 392-415.28 UNIVERSITY OF COLORADO STUDIES

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Physaria vitulfera, a tetraploid species of cruciferae

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Physaria vitulfera, a tetraploid species of cruciferae

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