JOURNAL OF THE ARNOLD ARBORETUMVOUIME 64 O)(TOiE 1983 NUMBER 4 STUDIES IN THE CRICIFERAE OF WESTERN NORTH AMERICA Ri:ED C. RoLLINS Si(NIFlIC NT NE.W TAXA of the family C'ruciferae keep surfacing as a result ofthe search for rare and endangered species. This work. under the auspices ofvarious federal government agencies and state natural heritage programs, isaccompanied by the renewed interest of both amateurs and professionals inthe native flora and fauna. In the western United States participants are gettinginto areas never before explored by botanists. and some of the resulting dis-coveries are spectacular (Rollins. 1982). Although the western United Statesis one of the principal centers of diversity for the Cruciferac and the area mighttherefore be expected to yield an occasional taxon nexer before seen, the numberbeing brought to light is almost an embarrassment considering that I have beenpursuing systematic studies on this family for more than 45 years. Of even greater interest than their newness, however, is the fact that someof these new taxa form the basis for an understanding of evolutionary pathwaysheretofore not fully grasped. For example, the silique morphology of Ph'sariaobcordata Rollins, a new species described below. helps to explain how speciesof Pht.saria (Nutt.) A. Gray have evolved an added mode of seed dispersalentirely different from that of their putative evolutionary progenitors in Les-querella S. Watson. It has generally been agreed (Payson. 1922; Rollins, 1939. 1950; Maguire &Holmgren. 1951: Mulligan. 1968: Rollins & Shaw. 1973) that Physaria is veryclosely related to Lesquerella and was probably derived from it evolutionarily.Of these two genera, Lesquerel/a contains the more primitive species; therefore.identifiable trends away from features characteristically present in that genuswould represent evolutionary changes-perhaps toward superior fitness forsurvival. The efficiency of seed dispersal is something that can be examined in thisconnection. In Lesquerella the valves of the siliques dehisce and fall away.leaving the seeds to fall more or less independently. Thus, the seeds are freedfrom the siliques to be dispersed by whatever agent is operative. In the regionc President and Fellows of Hararrd College. 1983..Journal o Ihe. I rnold .Irboretum 64: 49 -510. October. 1983.
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