Phylogeny and Biogeography ofPanaxL. (the Ginseng Genus, Araliaceae): Inferences from ITS Sequences of Nuclear Ribosomal DNA

Abstract

Panax,the ginseng genus, is one of the most medicinally important genera in the Orient and demonstrates a classical eastern Asian and eastern North American disjunct distributional pattern. Sequences of the internal transcribed spacers (ITS) and the 5.8S coding region of the nuclear ribosomal DNA repeat were obtained for the 12 species ofPanaxto reconstruct phylogenetic relationships. Of the 2 eastern North American species,P. quinquefoliusandP. trifolius, P. quinquefoliuswas suggested to be more closely related to the eastern Asian species in the ITS tree, whileP. trifoliuswas phylogenetically isolated. Monophyly of the three medicinally most important species,P. ginseng, P. notoginseng,andP. quinquefolius,suggested by previous workers, was not supported by the ITS data. A close phylogenetic relationship betweenPanaxandAraliawas supported. Several biogeographical implications were inferred: (1) two divergence events have produced the eastern Asian and eastern North American disjunct distribution inPanax;(2) no intercontinental species pairs are found inPanax;(3) a discrepancy between the sequence divergence pattern and the phylogenetic pattern was observed inPanax,suggesting the need for caution in using sequence divergence data alone in inferring biogeographical patterns; (4) the Himalayas and central and western China are the current centers of diversity of the ginseng genus; and (5) the low ITS sequence divergence and a close relationship among species in that region suggest that rapid evolutionary radiation may have created such a diversity ofPanaxin the Himalayas and in central and western China.