A phylogenetic analysis ofPanax (Araliaceae): Integrating cpDNA restriction site and nuclear rDNA ITS sequence data

A phylogenetic analysis ofPanax was performed using restriction site variations of eight PCR-amplified chloroplast regions. Twenty populations were examined, representing 13 of the 14 species ofPanax. Aralia cordata was used as the outgroup. The 11 restriction endonucleases produced a total of 105 restriction sites and length variations from the large single-copy region of cpDNA. Forty restriction variations are polymorphic. The cpDNA tree is largely congruent with the nuclear ribosomal ITS phylogeny. Similar to the ITS tree, the cpDNA dataset suggests the following relationships: (1)P. trifolius from eastern North America is sister to the clade consisting of all otherPanax species; (2)P. ginseng andP. japonicus from eastern Asia form a clade withP. quinquefolius from eastern North America; (3) the HimalayanP. pseudoginseng is most closely related toP. stipuleanatus of southwestern China; and (4) the medicinally importantP. notoginseng forms a clade with the closely relatedP. bipinnatifidus, P. ginseng, P. japonicus, P. major, P. quinquefolius, P. sinensis, P. wangianus, andP. zingiberensis. Two biogeographic disjunctions are detectable withinPanax. One is the connection of the eastern North AmericanP. trifolius with the rest ofPanax species. The other is the more recent disjunction between the North AmericanP. quinquefolius and the eastern AsianP. ginseng andP. japonicus. The active orogenies caused by the collision of the Indian Plate with Asia may have facilitated the diversification ofPanax taxa in Asia in the late Tertiary.