STUDIES IN THE GENUS LESQUERELLA

Abstract

PAYSON IN 1922 completed a thoroughly creditable monograph of Lesquerella which is the standard reference on the genus. Since then Fernald (1933), Munz (1929, 1932), Wiggins (1933), Peck (1934), and Cory (1930) have added new species, which together with those proposed in the present paper strongly indicate that this chiefly westAmerican genus is not entirely known even now. During several field seasons material of Lesquerella was collected for taxonomic and cytological investigation. The results of a study of this material, together with the description of a new variety collected in Alaska by Miss Edith Scamman, form the basis for the present report. The chromosome numbers summarized in table 1 were determined from aceto-carmen smears of root-tips and developing pollen. Specimens of each collection are in the Gray Herbarium of Harvard University. These data are not sufficient to form the basis for any general conclusions regarding the cytology of Lesquerella, but two significant points become clear. First, there is an apparent aneuploid relationship between species of Lesquerella, a condition not commonly found in the Cruciferae. According to Manton (1932), aneuploidy between species in the family is found chiefly in the Brassicinae. Second, polyploidy occurs naturally in at least some species of the genus. It is interesting to note that the polyploid L. ludoviciana from Mesa County, Colorado, exhibits the typical gigas characteristics often associated with plants possessing a multiple genom. Plants of this collection are several decimeters taller; the pedicels are more remote in the inforescence; the stellae are larger and form a less dense cover on plant parts, and the siliques are slightly larger than in the usual form of the species. Several species of Lesquerella. have been grown in the greenhouse for the purpose of observing their ontogenetic development and the effect of altered environmental conditions on the disposition of the indument over the plant surface. Those familiar 1 Received for publication March 29, 1939. with section Eulesquerella of the genus are aware that the plants of most species are literally encrusted with a dense covering of nearly orbicular stellae. It is a current problem in dealing with the systematic position of many varieties and species in the Cruciferae as to how much weight can be given to the presence or absence of an indumentum. Thus, by demonstrating the stability or lack of stability of this feature, some clue as to its usefulness as a taxonomic criterion should be obtained. In L. arctica var. Scammanae, L. subumbellata, L. intermedia, L. alpina, L. ovalifolia, and L. calcicola greenhouse plants were critically examined and compared with the specimens from which seed had been obtained in each instance. Particular attention was given to the abundance and disposition of the stellae. These were found to differ in no discernible way in the same species whether they were greenhouse grown or came from their natural habitat. From this we may roughly conclude that under greenhouse conditions of reduced sunlight and increased humidity, the abundance and disposition of the indument of Lesquerella is unaltered in firstgeneration plants. In connection with these observations, it was interesting to note that the cotyledons were in every case perfectly glabrous. The first pair of true leaves were always densely encrusted with stellae as in the later foliage. The following new entities have been discovered in Lesquerella in the past several years.