MOLECULAR PHYLOGENETICS AND EVOLUTION Vol. 6, No. 2, October, pp. 167–177, 1996 ARTICLE NO. 0069 Phylogeny and Biogeography of Panax L. (the Ginseng Genus, Araliaceae): Inferences from ITS Sequences of Nuclear Ribosomal DNA J UN WEN 1 AND E LIZABETH A. Z IM M ER Laboratory of Molecular Systematics and Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560 Received March 9, 1995; revised December 11, 1995 been repeatedly discussed by botanists and evolution- Panax, the ginseng genus, is one of the most medici- ary biologists since the time of Linnaeus (Boufford and nally important genera in the Orient and demon- Spongberg, 1983). In spite of the long history of interest strates a classical eastern Asian and eastern North in this biogeographical pattern, few studies have ex- American disjunct distributional pattern. Sequences plored the explicit phylogenetic relationships among of the internal transcribed spacers (ITS) and the 5.8S such disjunct species. Instead, morphological similari- coding region of the nuclear ribosomal DNA repeat ties and/or genetic divergence have usually been em- were obtained for the 12 species of Panax to recon- phasized (e.g., Li, 1952; Hara, 1952, 1956; Vogelmann struct phylogenetic relationships. Of the 2 eastern and Gastony, 1987; Parks and Wendel, 1990; Hoey and North American species, P. quinquefolius and P. trifol- Parks, 1991; Crawford et al., 1992). During Linnaeus’ ius, P. quinquefolius was suggested to be more closely era, many of these disjunct taxa were referred to as con- related to the eastern Asian species in the ITS tree, specific (Halenius, 1750) but were later recognized as while P. trifolius was phylogenetically isolated. Mono- vicariad sister species or species pairs (Li, 1972). Re- phyly of the three medicinally most important species, cent studies (Wen, 1991; Wen and Stuessy, 1993; Wen P. ginseng, P. notoginseng, and P. quinquefolius, sug- and Jansen, 1995) suggest that some of those vicariad gested by previous workers, was not supported by the sister species may not be as closely related as previ- ITS data. A close phylogenetic relationship between ously believed (e.g., Li, 1972). Panax and Aralia was supported. Several biogeo- Panax L. (Araliaceae), commonly known as the gin- graphical implications were inferred: (1) two diver- seng genus, is one of the approximately 120 genera of gence events have produced the eastern Asian and flowering plants with an eastern Asian and eastern eastern North American disjunct distribution in Pa- North American disjunct distribution (Wu, 1983). It nax; (2) no intercontinental species pairs are found in Panax; (3) a discrepancy between the sequence diver- consists of 12 species with 10 from eastern Asia and gence pattern and the phylogenetic pattern was ob- 2 from eastern North America. No rigorous or explicit served in Panax, suggesting the need for caution in us- phylogenetic analyses have been conducted for this ge- ing sequence divergence data alone in inferring nus although two competing hypotheses on evolution- biogeographical patterns; (4) the Himalayas and cen- ary relationships have been proposed, one based on tral and western China are the current centers of di- triterpenoids and seed morphology (Zhou et al., 1975) versity of the ginseng genus; and (5) the low ITS se- and the other based on chromosomal data (Yang, 1981). quence divergence and a close relationship among Delimitation of the Asiatic species is controversial species in that region suggest that rapid evolutionary (Hara, 1970; Hoo and Tseng, 1973, 1978; Zhou et al., radiation may have created such a diversity of Panax 1975) and a comprehensive taxonomic treatment is in in the Himalayas and in central and western China. progress (Wen, unpublished).  1996 Academic Press, Inc. Panax is one of the most medicinally important gen- era in the Orient, where almost every species of the ge- nus has been used as a source of medicine. Three of the species (P. ginseng, known as ginseng; P. quinquefolius INTRODUCTION or American ginseng; and P. notoginseng, commonly re- The disjunct distribution of congeneric plants be- ferred to as sanchi) are highly regarded medicines in tween eastern Asia and eastern North America has China and therefore widely cultivated. Ginseng liter- ally means the essence of man (Hu, 1976) and is known 1 Present address: Department of Biology, Colorado State Univer- as the lord or king of herbs. Although it is regarded sity, Fort Collins, CO 80523. 167 1055-7903/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved.