XVI International Botanical Congess

Generic boundaries among groups of Streptanthoid" species have lacked stability. Streptanthus, Caulanthus, Streptanthella, Guillenia, and others have frequently exchanged species. Currently, delimitation of the genera rests largely on characteristics of the siliques and seeds. In order to obtain a fresh perspective on phylogenetic relationships within and among these genera, I have been examining ITS sequence variation. Parsimony analyses involving sequences of 32 of the 45 Streptanthoid species indicate that Streptanthus and Caulanthus are highly paraphyletic with respect to each other, with the basal position poorly resolved. The results thereby cast doubt on the phylogenetic utility of the characters currently used for delimitation of these genera. The ITS phylogeny also suggests that serpentine endemism and perennial habit have evolved multiple times within the group.