Abstract: Paeonia, the only genus in the Paeoniaceae, consists of three sections and has 30 species(unpubl. revision)in the total. The section Moutan DC. , with all the six woody species in the genus, is confined to a small area in China from central Yunnan and E. Xizang (Tibet) to Anhui and Shaanxi. The section Onaepia Lindley, with only two species, is confined to western North America, from San Diego in California to the mountain Eldorad in Washington State, extending eastwards to Montana. The section Paeonia is the largest, with 22 species, widely distributed in the temperate zone of the Old World from Japan west-wards to Morocco and Portugal, but mainly in the Mediterranean region(12 species) and Eastern Asiatic region(6 species). Therefore E. Asiatic region and the Mediterranean region are two centres of species frequency of Paeonia, each with 12 species. The evolutionary trends of characters and primitive species or groups are inferred in this paper. It is considered that woody species, all in Sect. Moutan, are more primitive than herbaceous ones. In the latter characters, such as multiflowered stems, fewer leaflets and lobes, straight roots, diploid, are more primitive than solitary-flowered stems, more leaflets and lobes, fusiformthickened roots, tetraploid. The extant primitive forms are considered to have differentiated in E. Asiatic region, probably in central China, more precisely in the Qinling Range and its adjacent areas. The Mediterranean region might be the secondary differentiation centre of the genus. With the migration of the genus to the west and north, species with fusiformthickened roots and tetraploid increased. The section Onaepia is considered to have diverged directly from an ancient woody member not later than the Middle Miocene.

Key words: Paeonia, Differentiation center, Secondary diffrentiation center, Evolutionary trend, Distrubution pattern