East Asian-North American disjunctions and phylogenetic relationships within subtribe Nepetinae (Lamiaceae)
Özet
Biogeographic disjunctions, including intercontinental disjunctions, are frequent across plant lineages and have
been of considerable interest to biologists for centuries. Their study has been reinvigorated by molecular dating
and associated comparative methods. One of the “classic” disjunction patterns is that between Eastern Asia and
North America. It has been speculated that this pattern is the result of vicariance following the sundering of a
widespread Acrto-Teritary flora. Subtribe Nepetinae in the mint family (Lamiaceae) is noteworthy because it
contains three genera with this 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. Using four plastid and four nuclear markers, we estimated divergence times and
analyzed the historical biogeography of Nepetinae, including comprehensive sampling of all major clades for the
first time. We recover a well-supported and largely congruent phylogeny of Nepetinae between genomic compartments, although several cases of cyto-nuclear discordance are evident. We demonstrate that the three disjunctions are pseudo-congruent, with unidirectional movement from East Asia at slightly staggered times during
the late Miocene and early Pliocene. With the possible exception of Meehania, we find that vicariance is likely the
underlying driver of these disjunctions. The biogeographic history of Meehania in North America may be best
explained by long-distance dispersal, but a more complete picture awaits deeper sampling of the nuclear genome
and more advanced biogeographical models.
