Phylogeny And Polyploidy Of Genus Panax

Panax L.is a medicinally important genus within family Araliaceae,in which almost all species are of cultural significance for traditional Chinese medicine.It has been suggested that the East Asia and North America disjunct distribution of Panax has formed through two independent events and multiple rounds of whole genome duplications(WGD)might have occurred during the evolutionary process of Panax.In this study,we employed multiple chloroplast and nuclear markers to investigate the evolutionary history and diversification of Panax.Our phylogenetic analyses confirmed previous findings of the independent origins of disjunct distribution and both ancient and recent WGDs have occurred within Panax.The results of divergence time suggested that the ancient WGD might have occurred before the establishment of Panax.Then,at least two independent recent WGD events have emerged within Panax,one of which has resulted in the formation of three geographically isolated tetraploid species P.ginseng,P.japonicus and P.quinquefolius;the other event has occurred within the P.bipinnatifidus species complex.Population genetic analyses showed that the diploid species P.notoginseng harbored significantly lower nucleotide diversity than those of the two tetraploid species P.ginseng and P.quinquefolius and the three species showed distinct nucleotide variation patterns at exon regions.Our findings based on the phylogenetic and population genetic analyses,coupled with the species distribution patterns of Panax,indicated that the two rounds of WGD along with the geographic and ecological isolations might have together contributed to the evolution and diversification of this genus.