The Phylogenetic Status of Polyscias (Araliaceae) Based on Nuclear Its Sequence Data

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Abstract
The circumscription of Polyscias, the second largest genus in Araliaceae (∼130 species), has been broadened extensively in recent decades, but this circumscription has often been applied inconsistently, and no global treatment of the genus exists. To examine evolutionary relationships among the species of Polyscias, as well as the placement of this genus within Araliaceae, phylogenetic analyses were performed on a data set of 84 ITS sequences (from nuclear ribosomal DNA), including sequences from five of the formal sections of Polyscias and a representative sample of taxa from throughout Araliaceae and allied families. Results suggest that Polyscias is highly paraphyletic: members of nine other genera (Gastonia, Cuphocarpus, Arthrophyllum, Reynoldsia, Tetraplasandra, Munroidendron, Meryta, Pseudopanax, and Schefflera p.p.) are found nested within a broad "Polyscias sensu lato" clade. Despite a lack of support for the current definition of the genus, the phylogenetic relationships suggested by ITS data are remarkably consistent with geographic distributions. Three clades are clearly centered in the western Indian Ocean basin, and five others in the Pacific. These data further suggest that Polyscias sensu lato may have arisen in tropical Australasia, whence they may have migrated both east to the Pacific and west to the Indian Ocean, probably via long-distance dispersal after the breakup of Condwanaland. Expanded studies, however, are required to address these biogeographic issues and to develop a revised generic-level taxonomy for Polyscias and its allies.

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