Astragalus (loco weed) is the largest genus of flowering plants in the world and is especially well represented in western North America, where there are over 400 species. Nevertheless, its species have rarely been the subject of a biosystematic study. Nine closely related annual members of the genus, native to Arizona, California, and Nevada, have been chosen as an appropriate group for such a study. The extent of morphological divergence in the fruits and flowers of these plants, reflected in their previous assignment to three different genera, is quite remarkable. The objective of the proposed research is to examine the evolutionary processes which have brought about and preserved this diversity. Specifically, this study will 1) clarify phylogenetic relationships among the members of the study group based on anatomical, cytological, and genetic data, and 2) use data derived from the analysis of genetic variation to evaluate breeding systems, speciation processes, and levels of divergence in the group.
