The evolution of Araliaceae: A phylogenetic analysis based on ITS sequences of nuclear ribosomal DNA

Phylogenetic analyses of ITS sequence data from 70 species and 40 genera of Araliaceae (representing all major lineages within the "core group" of the family) do not support the widely used traditional division of Araliaceae into three tribes. Tribe Aralieae (characterized by imbricate petals) is fo und nested within a paraphyletic Schefflerieae (whose taxa have valvate pet als). There are, however, two large monophyletic groups comprising most ara liad genera: the "Aralia-Polyscias-Pseudopanax group" (which includes Arali a, Meryta, Munroidendron, Panax, Pentapanax, Polyscias, Pseudopanax, Reynol dsia, Sciadodendron, Tetraplasandra, and their close allies), and the "Eleu therococcus-Dendropanax-Schefflera group'' (including Brassaiopsis Dendropa nax, Eleutherococcus, Fatsia, Hedera Oreopanax, Schefflera, Sinopanax, and their close allies). The ITS trees also permit a re-evaluation of several t axonomically important morphological characters (e.g., petal aestivation, l eaf architecture, carpel number, and habit), and provide the opportunity to assess traditional generic delimitations in the family. Four of the larges t genera appear to be either polyphyletic (Schefflera, Pseudopanax) or para phyletic (Aralia, Polyscias), but further studies will be needed to fully r e-define these complex taxa. Outgroup comparisons and the placement of Astr otricha and Osmoxylon (in basally-branching lineages in Araliaceae) help to confirm a paleotropical origin of the family. The ITS topologies suggest t hat biogeographic radiations into different tropical/subtropical regions an d into the north and south temperate regions occurred early in the history of core Araliaceae. Temperate taxa have arisen several times independently from tropical and subtropical relatives, although a few subtropical taxa ma y be found nested within temperate clades (e.g., Pentapanax within Aralia). Migrations between the Old and New Worlds are also suggested for several t axa, including Aralia, Panax, Oplopanax, and the Sinopanax-Oreopanax generi c pair.