PHYLOGENY AND BIOGEOGRAPHY OF ARALIA SECT. ARALIA (ARALIACEAE)

Aralia sect. Aralia (Araliaceae) consists of approximately eight speci es disjunctly distributed in Asia and North America. Phylogenetic and biogeographic analyses were conducted using sequences of the internal transcribed spacer regions of the nuclear ribosomal DNA. Aralia racemo sa from eastern North America was sister to A. californica from wester n North America. Aralia cordata from eastern Asia did not form a speci es-pair relationship with the eastern North American A. racemosa. The two subspecies of A. racemosa formed a monophyletic group. Biogeograph ic analyses showed a close area relationship between eastern North Ame rica and western North America. The Himalayas were cladistically basal and eastern Asia was placed between the Himalayas and North America. The biogeographic analysis supported the origin of the eastern Asian a nd eastern North American disjunct pattern in Aralia sect. Aralia via the Bering land bridges. Comparisons with results of phylogenetic anal yses of other genera suggested that (1) the floristic connection betwe en eastern North America and western North America may be stronger tha n previously thought; and (2) the biogeographic patterns in the Northe rn Hemisphere are complex. Furthermore, a lack of correlation between sequence divergence values and phylogenetic positions was observed, su ggesting the importance of a phylogenetic framework in biogeographic a nalyses.