PLUNKETT, GREGORY M.1*, PORTER P. LOWRY II2, AND JONATHAN M. EIBL1. 1Department of Biology, Virginia Commonwealth University, Richmond, VA 23284-2012, and 2Missouri Botanical Garden, St. Louis, MO 63166-0299. - Phylogenetic relationships of Schefflera and Polyscias: non-monophyly in the two largest genera of Araliaceae.
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