Internal transcribed spacer phylogeny of the Asian and eastern North American disjunct Aralia sect. Dimorphanthus (Araliaceae) and its biogeographic implications

Sequences of the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA were used to generate a phylogenetic hypothesis for the Asian and eastern North American disjunct Aralia sect. Dimorphanthus. The ITS phylogeny supports the transfer of Aralia hispida of sect. Hispidae to sect. Dimorphanthus to maintain the monophyly of the latter The north temperate series Dimorphanthus was paraphyletic, with the subtropical and tropical series Chinensis and Foliolosae nested within. This pattern of differentiation is consistent with the hypothesis of morphological stasis among the closely related disjunct taxa between eastern Asia and eastern North America in series Dimorphanthus. There is a lack of direct intercontinental sister species relationship in the section. The eastern North American taxa (Aralia spinosa and A. hispida) are cladistically basal, and the Asiatic taxa form a clade, which indicates that the formation of the intercontinental disjunction was prior to the diversification of Asiatic taxa. Fossil evidence indicated that the disjunct pattern originated during the Miocene or earlier.