Phylogeny of Camassia (Agavaceae) Inferred from Plastid rpll6 Intron and trnD-trnY-trnE-trnT Intergenic Spacer DNA Sequences: Implications for Species Delimitation

Camassia is a genus of six bulb-forming species endemic to North America that have figured prominently in the culture and sustenance of native peoples. In western North America they form a conspicuous element of wet meadows and forest openings. Species and, especially, subspecies delimitations have been problematic. Further, several hypothesized phylogenetic and biogeographic scenarios for the origin and diversification of the genus remain untested. We estimated the phylogeny of Camassia using two noncoding plastid DNA regions: rpll6 intron and trnD-trnY-trnE-trnT spacers, with the goals of evaluating 1) the delimitation of species and 2) Gould's hypotheses for the origin of species and infraspecific taxa. Maximum parsimony and Bayesian analyses provided concordant estimates of the phylogeny consistent with the monophyly of eastern American C. scilloides and western American C. howellii and C. leichtlinii. Two western American species were found to be paraphyletic— C. cusickii weakly so, but C. quamash was strongly supported as paraphyletic to C. cusickii, C. scilloides and C. angusta. Our results are largely consistent with Gould's views that the genus originated in southwestern Oregon and diversified through eastern migration, and that C. scilloides and C. cusickii are derived from within C. quamash. Despite evidence that Camassia species hybridize, by sampling sympatric populations we detected only a single case of introgression of plastid haplotypes. This study provides the first molecular phylogenetic and phylogeographic context for evaluating evolutionary process and trait variation in this iconic genus of western North America.