Phylogeny and phytogeography of Eupatorium (Eupatorieae, Asteraceae): Insights from sequence data of the nrDNA ITS regions and cpDNA RFLP

The relationships of eastern North American-eastern Asian-European disjunct s in the genus Eupatorium were examined by sequencing the internal transcri bed spacers (TTS) of nuclear ribosomal DNA and restriction site analysis of chloroplast DNA, Molecular data provided strong evidence that (1) this gen us originated in North America, (2) the genus diverged into three morpholog ical species groups, Eutrochium, Traganthes and Uncasia in North America, a nd (3) one of the North American Uncasia lineages migrated into temperate E urope and eastern Asia over the Bering land bridge. The estimated divergenc e times support a late Miocene to early Pliocene migration from North Ameri ca to Eurasia via the Bering land bridge. A European species was sister to all of the eastern Asian species examined. The disjunct distribution patter n of the genus Eupatorium is incongruent with the classical Arcto-Tertiary geoflora concept.