A phylogenetic analysis of Panax (Araliaceae):: integrating cpDNA restriction site and nuclear rDNA ITS sequence data

A phylogenetic analysis of Panax was performed using restriction site variations of eight PCR-amplified chloroplast regions. Twenty populations were examined, representing 13 of the 14 species of Panax. 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 other Panax species; (2) P. ginseng and P. japonicus from eastern Asia form a clade with P. quinquefolius from eastern North America; (3) the Himalayan P. pseudoginseng is most closely related to P. stipuleanatus of southwestern China; and (4) the medicinally important P. notoginseng forms a clade with the closely related P. bipinnatifidus, P. ginseng, P. japonicus, P. major, P. quinquefolius, P. sinensis, P. wangianus, and P. zingiberensis. Two biogeographic disjunctions are detectable within Panax. One is the connection of the eastern North American P. trifolius with the rest of Panax species. The other is the more recent disjunction between the North American P. quinquefolius and the eastern Asian P. ginseng and P. japonicus. The active orogenies caused by the collision of the Indian Plate with Asia may have facilitated the diversification of Panax taxa in Asia in the late Tertiary.