Oral Paper

         Biogeography

East Asian-North American disjunctions and relationships in Nepetinae (Lamiaceae)

Presenting Author
Bryan Drew
Description
Biogeographic disjunctions are found across plant lineages and have been of major interest to biologists for centuries. Research on this subject has been reinvigorated by recent advances in molecular dating and associated comparative methods. One of the “classic” disjunction patterns is that between Eastern Asia and Eastern/Western North America. It has been speculated that this pattern is the result of vicariance following the sundering of a widespread Acrto-Teritary flora. The subtribe Nepetinae in the Lamiaceae (mint family) is noteworthy because it contains three genera with this intercontinental disjunction pattern: Agastache, Dracocephalum, and Meehania. These disjunctions are ostensibly the result of three separate events, allowing for concurrent testing of the tempo, origin, and type of each biogeographic event. We use phylogenies based on chloroplast and nuclear data to estimated divergence times and analyze the historical biogeography of Nepetinae. We show that the three disjunctions are “pseudo-congruent”, with unidirectional movement from East Asia to North America occurring at slightly staggered times during the late Miocene and early Pliocene, about 3.5-10 million years ago. With the possible exception of Meehania, we find that vicariance is likely the underlying driver of the disjunctions.