Over the past several decades, taxonomic re-alignments in Araliaceae have resulted in a dramatic expansion in the size of the two largest genera, Schefflera (~650 spp.) and Polyscias (~130 spp.). As currently circumscribed, these genera now represent nearly two thirds of the species diversity in the family. The large size (relative to other araliad genera) and mostly Gondwanan distribution of both Schefflera and Polyscias make these genera good model systems for a variety of diversification studies, including the study of speciation rates and biogeographic patterns. Although taxonomic systems have often been used as the basis for such studies, it is now widely accepted that robust phylogenetic reconstructions are needed to test alternative evolutionary hypotheses. Preliminary data based on the internal transcribed spacers (ITS) of nuclear ribosomal DNA suggest that neither Schefflera nor Polyscias is monophyletic, a finding that will have important implications for both taxonomic and diversification interpretations. More specifically, ITS data suggest that Schefflera is polyphyletic, forming at least three (and perhaps many more) unrelated clades within Araliaceae. These clades do, however, exhibit geographic structuring (and in some cases form sister groups with other araliad taxa from the same geographic region). The data also suggest that Polyscias is paraphyletic; no fewer than six additional genera (Reynoldsia, Tetraplasandra, Munroidendron, Arthrophyllum, Gastonia, and Cuphocarpus) are derived from within a broad Polyscias sensu lato clade. As in Schefflera, the several groups of Polyscias s. lat. are geographically structured, with one broad subclade centered on Madagascar (and the Indian Ocean basin in general), and several additional subclades centered in the Pacific. Preliminary biogeographic analysis suggests these clades may have been derived from repeated dispersal events from Australasia.

Key words: Araliaceae, biogeography, ITS nrDNA, Polyscias, Schefflera