Molecular phylogenetic and biogeographic study of the genus Artemisia (Asteraceae), with an emphasis on section Absinthium

Artemisia is the largest genus in the tribe Anthemideae and is composed of ecologically, morphologically, and chemically diverse species found primarily throughout the Northern Hemisphere. Delimitation within Artemisia and among allied genera in subtribe Artemisiinae has been difficult, but previous phylogenetic analyses have helped clarify some major lineages and sister relationships. Despite these contributions, many questions remain unanswered regarding the monophyly of certain taxonomic groups, relationships among New and Old World species, and migration history of the genus. The objectives of this investigation were to reexamine the classification and biogeography of Artemisia, with an emphasis on section Absinthium , in greater detail compared to earlier studies and to evaluate the utility of thirteen different chloroplast regions for inferring phylogenetic relationships. Ingroup and outgroup taxon sampling was greatly increased over previous studies and included most New World taxa of Artemisia and Sphaeromeria, more Asian species, and multiple accessions of widespread species and species from the Arctic, Beringia, and islands and archipelagos in the North Pacific. The molecular ITS phylogeny contained 194 accessions of 173 taxa (91 sequences of 73 taxa were new and the remaining from GenBank) and showed that Artemisia and its traditional infrageneric groups are not monophyletic as currently circumscribed. Artemisia is paraphyletic by the exclusion of several small segregate genera from Asia and the North American genus Sphaeromeria. Results from the chloroplast survey showed that the psbA-trnH and rpl32-trnL spacers provided the most parsimony-informative characters. Chloroplast phylogenies using these two markers were constructed with a reduced dataset that included members of Artemisia section Absinthium and exemplars from major clades identified in the ITS-based phylogeny. Plastid sequence data, though less variable and informative, largely corroborated the ITS results. The molecular data suggests that North American Artemisia species have multiple origins, and that western North America has served as a source for some colonizing elements in eastern Asia and South America. This study further identifies Beringia not only as an important migration corridor for the bi-directional exchange of New and Old World species, but also as a secondary center of diversity and source area for the genus Artemisia in the Arctic.