The "Streptanthoid" genera of tribe Thelypodieae (Brassicaceae) currently comprise about 60 species of annual to perennial wildflowers of the U.S. midwest to southwest, and include Streptanthus, Caulanthus, Guillenia, and Streptanthella.  Extensive morphological diversity, primarily in floral features, has set this group apart from its relatives in the Thelypodieae but has hindered attempts at establishing a stable classification of its members.  Sequences of the ITS region and ndhF were analyzed separately and jointly with the goal of resolving relationships within and among the genera of the group.  Results of the analyses provide support for the monophyly of subgenus Streptanthus, as well as several of the sections within subgenera Euclisia and Pleiocardia of Streptanthus.  Moreover, most clades of streptanthoid species have clear geographic bases.  The distinctness of Streptanthus from Caulanthus, however, is not supported, thereby casting doubt on the value of the features traditionally used to distinguish the two genera: fruit shape, cotyledon position, and presence of seed wings.  The results also suggest that Guillenia, a genus recently restored within the group, is not monophyletic.

Key words: Brassicaceae, ITS, ndhF, Thelypodieae