Infrafamilial classifications and characters in Araliaceae: Insights from the phylogenetic analysis of nuclear (ITS) and plastid (trnL-trnF) sequence data

Abstract.

Traditional classifications of Araliaceae have stressed a relatively small number of morphological characters in the circumscription of infrafamilial groups (usually recognized as tribes). These systems remain largely untested from a phylogenetic perspective, and only a single previous study has explicitly explored intergeneric relationships throughout this family. To test these infrafamilial classification systems, parsimony and Bayesian-inference analyses were conducted using a broad sampling of 107 taxa representing 37 (of the 41) genera currently recognized in core Araliaceae, plus five outgroup genera. Data were collected from two molecular markers, the internal transcribed spacers (ITS) of the nuclear rRNA genes and the intron and intergenic spacer found in the trnL-trnF region of the chloroplast genome. The results suggest that there are three major lineages of Araliaceae, and that these lineages generally correspond with the centers of diversity for the family. The Aralia and Asian Palmate groups are centered primarily in eastern and southeastern Asia, whereas the Polyscias-Pseudopanax group is found throughout the Pacific and Indian Ocean basins. Several poorly resolved lineages are placed at the base of core Araliaceae, and the geographic distributions of these clades are consistent with a hypothesized rapid radiation of Araliaceae, possibly correlated with the breakup of Gondwanaland. Comparison of molecular results with the traditional systems of classification shows almost no congruence, indicating that they inadequately reflect phylogenetic relationships. Moreover, the morphological characters employed in these classifications appear to be highly homoplastic, and are thus of little utility at the infrafamilial level.