Evolution of Polyscias sect. Tieghemopanax (Araliaceae) based on nuclear and chloroplast DNA sequence data

Polyscias sect. Tieghemopanax comprises approximately 26 species almost entirely endemic to New Caledonia. Three independent molecular markers were used to infer phylogenetic relationships and evolutionary patterns within the Tieghemopanax group, and to evaluate the status of a single highly variable species, P. dioica. Sequence data from nuclear ribosomal ITS and 5S spacers along with intron and spacer sequences from the plastid trnL-F region were analyzed separately and in each possible combination of the three data sets. Combined analyses provided topologies largely congruent with each of the separate analyses but with increased resolution, higher bootstrap support, and decreased computational time. The resulting cladograms confirm the monophyly of section Tieghemopanax and suggest an allopatric or adaptive divergence model of speciation in response to geography, elevation, and/or substrate type for most species. In contrast, P. dioica may represent an assemblage of once distinct but closely related species whose boundaries have recently broken down through hybridization and introgression. The results suggest that the Tieghemopanax group originated and diversified on New Caledonia (23 spp.); subsequent long-distance dispersal to other archipelagos resulted in the evolution of three local endemics (1 sp. each in Vanuatu, Fiji, and Australasia) and the widespread distribution of P. cissodendron in the SW Pacific.