The phylogeny of the Aralia–Panax clade (Araliaceae) was constructed with four data sets: morphology, nuclear ribosomal ITS regions, and the chloroplast ndhF gene and the trnL-F region. The morphological and the chloroplast trees place Panax sister to the Aralia clade. The ITS data, however, suggest that Panax is nested within Aralia. Aralia sect. Pentapanax (formerly the genus Pentapanax) is nested within sect. Dimorphanthus. The diversification of major lineages of the Aralia-Panax clade seems to correlate with ecological habitats. Species of Aralia sect. Dimorphanthus seem to have adapted to sunny habitats; those of sect. Pentapanax are mostly epiphytic on forest trees; taxa of sect. Aralia and the genus Panax are forest perennial herbs; and those of sect. Humiles seem to have adapted to the dry semi-desert of southwestern North America and central America. The diversification of the major lineages into different habitats seemed to be rapid. Biogeographically the Aralia-Panax clade shows three major disjunctions between Asia and North America. The evolution of the intercontinental biogeographic disjunctions is discussed based on the phylogenetic patterns, molecular sequence divergence, and fossil evidence. Diversification rates in Asia and North America were estimated. Asia showed a substantially higher rates of speciation than North America within the Aralia-Panax clade.

Key words: Aralia, Araliaceae, biogeography, diversification, Panax, phylogeny