Monophyly and major clades of Meryta (Araliaceae)

Phylogenetic analyses of nuclear ribosomal ITS and ETS sequences yield considerable improvements in our knowledge of relationships, character evolution, and biogeography in Meryta (Araliaceae). This genus comprises ca. 30 species, all of which share simple leaves and a dioecious sexual system, a unique combination in Araliaceae. Meryta is distributed widely across the Pacific, but each of its species is endemic to only one or a few islands. Previous phylogenetic studies have included only a very limited number of exemplars from Meryta, but have suggested that the genus is related to the Southwest Pacific clade of Schefflera within the larger Polyscias-Pseudopanax group of Araliaceae. Our data confirm this previous placement and provide evidence for the monophyly of Meryta. There is no support for the recognition of three segregate genera, Botryomeryta, Schizomeryta, and Strobilopanax. Within Meryta, we have identified two major clades, one that unites the species from Fiji and New Zealand (both of old geological origin), and a second, "Northern Arc clade" comprising the remaining species of Meryta. In this second clade, several subclades of New Caledonian species can be recognized, along with a "Volcanic Islands subclade." The presence of species in New Caledonia, Fiji, and New Zealand, together with the placements of these species in the phylogenetic trees, is suggestive of an ancient vicariance, whereas the distribution of the members of the Volcanic Islands subclade appears to be best explained by a series of long-distance dispersal events, most likely from New Caledonia.