Species in Mimulus in western North America have become model systems for the study of evolutionary processes in nature. As currently described, Mimulus contains approximately 120 species, of which 75 percent occur only in western North America. Mimulus contains species with different ploidy levels, reproductive strategies, and pollination syndromes. Molecular phylogenetic studies in Mimulus have redefined Phrymaceae and indicate that at least six genera have been derived from within Mimulus. One clade recovered in these analyses contains all of the species of Mimulus in western North America, plus Hemichaena, Berendtiella, and Leucocarpus. A phylogenetic hypothesis for 82 species was estimated using ITS, ETS and trnL sequences. These analyses indicate that polyploidy has evolved independently at least six times, woody plants have evolved from herbaceous ancestors twice, self-pollination has possibly evolved 10 times and hummingbird pollination has evolved at least three times. These results also indicate that Mimulus has established twice in Asia and once in South America from ancestors in western North America. Within sect. Eunanus patterns of genetic diversification better match geographic distribution (Sierra Nevada versus the Pacific Northwest) than taxonomic circumscription. Mimulus nanus is not monophyletic in two distinct ways. First, individuals from the Sierra Nevada are distinct from those in the Cascade and Rocky Mountains. Second, Mimulus nanus in the Pacific Northwest is paraphyletic, because three currently recognized species, M. cusickii, M. jepsonii, and M. clivicola have been derived from within it.

Key words: Mimulus nanus, Mimulus, Phrymaceae, pollination biology, polyploidy