Phylogeny, biogeography, and morphological evolution among and within the Neotropical and Asian clades of Schefflera (Araliaceae)

Schefflera is the largest and most complex genus of Araliaceae, with ~600
described species (and many additional species awaiting formal
description), but recent studies indicate that it is polyphyletic, forming
five geographically centered clades spread across the major lineages of
the family. Significant progress has been made in revising the three
smallest clades, but the two largest groups, centered in Asia and the
Neotropics, remain poorly understood. To advance our knowledge of these
groups, a taxon set of 211 Schefflera samples and 38 samples representing
other genera of Araliaceae (including all genera of the “Asian Palmate
clade”) was assembled, from which sequences were obtained for six DNA
spacer regions, including two nuclear (ITS, ETS) and four plastid markers
(rpl32-trnL, trnF-rpl32, trnK-rpl16, psbA-trnH). Results were compared to
an informal system of classification based on morphology. They confirm the
monophyly of both the Asian and Neotropical groups, and their inclusion
within the Asian Palmate clade, but not as sister groups. In the
Neotropical clade, five major subclades can be recognized, four
corresponding closely to morphological groupings (Cephalopanax,
Crepinella, Didymopanax, Sciodaphyllum) and one that is geographically
coherent (Gleasonia). Within Asian Schefflera, there are four major
subclades, corresponding closely to currently recognized informal groups
(Agalma, Heptaphyllum, Heptapleurum, Hypoleucoi). Biogeographic analyses
suggest that both the Asian and Neotropical groups can trace their origins
to SE Asia, where Asian Schefflera is still well represented and where
Chengiopanax, the possible sister group of Neotropical Schefflera, is
native. Trait-evolution analyses of a remarkable series of convergences in
habit, foliar, and reproductive characters suggest multiple independent
origins (and some reversals), both within and between the Neotropical and
Asian clades of Schefflera.