Phylogeny and biogeography of Asian <I>Schefflera</I> (Araliaceae) based on nuclear and plastid DNA sequences data

Abstract

The phylogeny of Asian Schefflera was inferred from sequences of the nuclear ribosomal internal transcribed spacer (ITS) region, and six plastid regions (the ndhF gene, the trnL-trnF region, the rps16 intron, the atpB-rbcL intergenic spacer, the rpl16 intron, and the psbA-trnH intergenic spacer). Phylogenetic analyses of the combined plastid and ITS data with parsimony and Bayesian methods strongly support the monophyly of Asian Schefflera. The genus is supported to be closely related to Heteropanax and Tetrapanax with the small tropical continental Asian genus Heteropanax as its sister. Within Asian Schefflera, four distinct subclades were identified: (1) the widely distributed Asian Heptapleurum group with no styles in the gynoecium, (2) the main Agalma group with racemose or spicate inflorescence units with a few umbellate taxa, (3) the Schefflera hypoleuca group, and (4) the Schefflera heptaphylla group. In a broader phylogenetic framework of Araliaceae, Asian Schefflera is hypothesized to have originated in continental Asia at 57.41 mya (95% high posterior density HPD] interval of 40.33–76.06 mya) in the early Tertiary and radiated into the now SE Asia, eastern Himalaya, and E Asia at 46.11 mya (95% HPD: 33.02–60.69 mya). Its subsequent diversification in Asia may have been driven largely by the collision of the Indian plate with the Asian plate in the middle Eocene and the collision of the Australian margin with the Eurasian margin in the early Miocene.