Sequence data for the ITS region of rDNA provide evidence that Linanthus bicolor, an annual species of western North America, is polyphyletic. A previous study identified two sequence types, distinguished by over 50 fixed nucleotide differences, in populations from different geographical regions. Phylogenetic analysis revealed that the two are not sister taxa and, furthermore, that each represents an independent origin of self-fertilization. The morphological similarity of the two taxa, especially in floral traits, is hypothesized to have resulted from convergent evolution in characters associated with self-fertilization. Morphological and genetic data for populations sampled throughout the range of L. bicolor indicate that these distinct genetic types correspond to intraspecific taxa as currently circumscribed. The molecular evidence for polyphyly of L. bicolor, presence of significant morphological differences between the two taxa, and evidence that they are, to a large extent, reproductively isolated provide a strong rationale for distinguishing them at the level of species. We propose that L. bicolor var. minimus be elevated to species status with the designation, L. minimus.

Communicating Editor: Jeff H. Rettig