Molecular phylogeny of Artemisia section Tridentatae (Asteraceae) based on chloroplast DNA restriction site variation

Chloroplast DNA restriction site variation was used to examine phylogenetic relationships in Artemisia sect. Tridentatae, a complex of eleven species of woody shrubs, which are dominant components of sagebrush communities of western North America. Twenty-seven endonucleases were utilized to identify 82 variable site mutations, 27 of which were phylogenetically informative. The resulting cpDNA phylogeny indicates that sect. Tridentatae is monophyletic, with the exception of A. palmeri and A. bigelovii, two historically anomolous species. A sister-group relationship between A. palmeri and species of subg. Artemisia supports the exclusion of A. palmeri from sect. Tridentatae (subg. Seriphidium), and its inclusion within subg. Artemisia. Artemisia bigelovii, a species with heterogamous capitula, is nested within the Tridentata clade, supporting its inclusion within the section. Introgression and subsequent chloroplast capture of the Tridentatae genome by two unrelated species, A. californica and A. fihlifolia, may explain the unexpected placement of these two species in the Tridentata clade. Low cpDNA sequence divergence provides only limited resolution of phylogenetic relationships within sect. Tridentatae, indicative of a recently differentiated and/or hybridizing polymorphic species complex. In addition, the cpDNA data provide only equivocal evidence for either of two competing hypotheses regarding the origin and phylogenetic relationship of sect. Tridentatae within Artemisia s.l.