Abstract
The genus Tauschia has long been a source of taxonomic consternation for researchers. The group of species currently included in this genus are distributed primarily across the western United States and Mexico, but a few species occur in Central America and northern South America. Its circumscription is highly problematic, and its species have been moved countless times between more than a dozen genera. The advent of molecular phylogenetics has allowed some testing of generic boundaries in Tauschia and related taxa, but the sampling of previous studies was limited to a few species representing too small of a range to sort out the confusion. Here, we expand the sample size to include plants from throughout the range of the genus and use this to examine relationships among species of Tauschia , as well as to the larger clades to which it belongs within tribe Selineae. We also detail the complex taxonomic history of Tauschia and related genera, provide a complete synonymy of the genus as it is currently defined, and confirm the polyphyly of Tauschia via phylogenetic analysis of nuclear and cpDNA sequences.