The North American endemic genus Nemophila (Hydrophyllaceae) consists of 11 species and six varieties of annual herbs found primarily in California. Nine species occur in the western United States as far south as Baja California, while two species (N. phacelioides and N. aphylla) are disjunct in the southeastern United States. The evolutionary relationships within Nemophila remain unclear despite eight previous taxonomic treatments and exploration of a variety of potentially useful kinds of characters (morphology, cytology, and development). We present a phylogenetic analysis of Nemophila and relevant taxa in the tribe Hydrophylleae using DNA sequence data from both the nuclear ribosomal DNA internal transcribed spacer, and from the chloroplast 3 trnK intron. The molecular phylogenetic analyses concur with infratribal relationships previously inferred from seed coat characters. On our phylogeny Nemophila and Pholistoma form an unresolved polytomy, but seed coat morphology suggests that Pholistoma is sister to Nemophila as a whole. Within Nemophila seven of the eight Californian species form a strongly supported clade; the remaining taxa occur as a second, weakly supported clade. Nonetheless, in resolved phylogenies, the two southeastern species are never sister taxa and thus may have resulted from independent dispersal or vicariant events. However, additional data are needed to confirm that these species are indeed not sister taxa.

Key words: Hydrophyllaceae, Nemophila, Pholistoma, phylogeny