Penstemon subg. Dasanthera (Scrophulariaceae) is a small group comprising 17 taxa distributed at high elevations in western North America. The subgenus is characterized by a woody habit and lanate pubescence on the anther surfaces. Hybridization has played a significant role in the evolution of the subgenus. Phylogenetic and biogeographic relationships within subg. Dasanthera are being examined using nrITS and matK sequence data. Sequence divergence is very low for both ITS (mean=0.0086) and matK (mean=0.0046). However, these data suggest that subg. Dasanthera represents the earliest divergence in Penstemon. Furthermore, the monophyly of the subgenus is supported. Both data sets suggest an origin of Penstemon in the northern Rocky Mountains, followed by westward migration and radiation of subg.Dasanthera in the Cascade and Sierra Nevada Mountains. These data are insufficient for resolving relationships among the Cascade/Sierra Dasanthera penstemons. To examine evolutionary relationships among the Dasanthera penstemons, inter-simple sequence repeat (ISSR) have been utilized to examine species relationships. Five primers were surveyed for 128 individuals representing all species of Penstemon subg. Dasanthera. A neighbor joining tree was produced using a similarity matrix constructed from Dice's coefficient. In addition, the potential for use of ISSR fragments in cladistic analyses have been examined. This study suggests the utility of ISSR markers for examining evolutionary relationships and patterns of introgression among closely-related taxa.

Key words: Biogeography, Hybridization, ISSR, ITS, matK, Penstemon