A phylogeny of Thermopsideae (Leguminosae: Papilionoideae) inferred from nuclear ribosomal internal transcribed spacer (ITS) sequences

Based on nuclear ribosomal DNA internal transcribed spacer (ITS) sequences, Thermopsideae is phylogenetically studied within a genistoid background. Analysis reveals that the tribe is not supported as a monophyletic group. Some species of Sophora s.s are nested within it. The central Asian desert Ammopiptanthus forms an isolated clade but is relatively remote to other Thermopsideae members. Piptanthus, Anagyris, Baptisia, and Thermopsis are clustered together into a robust clade. We hence propose that the tribe could either be reduced to just the four 'core genera' with Ammopiptanthus excluded, or, as an alternative, that Thermopsideae could become part of a new Sophoreae s.s. if it is re-circumscribed in the future. Both Piptanthus and Baptisia appear as monophyletic. The genus Anagyris is closer to some east Asian Thermopsis species than to Piptanthus. The east Asian and North American disjunct Thermopsis is not monophyletic. The ITS results suggest a geographical division between the Old World and New World Thermopsis. The east Asian species are clustered with Piptanthus and Anagyris, whereas the North American species are allied to Baptisia. Nonetheless, the only two north-eastern east Asian native Thermopsis species appear to be more related to the North American group than to the east Asian one. The related biogeographical significance has therefore been additionally discussed. (c) 2006 The Linnean Society of London.