Abstract: Abstract 1. It was observed that somatic chromosome numbers of four species of the genus Panax L. are as follows: Panax japonicus 2n=24, P. notoginseng 2n=24, P. ginseng 2n=44 and P. quinquefolius 2n=48. The somatic chromosome numbers of P. japonicus from Lushan and Jinggangshan (Jiangxi Province, China) is different from that of Japanese population (2n=48). The chromosome numbers (2n=24) of P. notoginseng is first reported. 2. The P. japonicus, one of the diploid species, which has the widest geographical distribution is perhaps the more primitive type among the living species of Panax. While, the P. ginseng and P. quinquefolius, the tetraploid species, are more advanced types than the diploid species. The conclusion from cytotaxonomy is thus different from that of chemical taxonomy. 3. The cytological analysis together with the geographic distribution of this four species shows that the Southwestern China is the modern distribution center, also the most variational center, and perhaps the center of origin for the genus Panax L.