The classification and geographical distribution of Betulaceae of Yunnan province

Betulaceae growing in Yunnan province consists of 2 genera,16 species and 1 variant.Genus Alnus is divided into two sections,i.e.sect.Alnus(1 species) and sect,Cremastogyne(2 species).Betula is newly divided into two sections;sect.Betula(7 species of two subsections) and sect.Chinenses(6 species and 1 variant). From the study of the geographical distribution of these species,we may come to the following conclusions:1) the family of Betulaceae seems to originate from western Yunnan;2) from the distributive center,the species of Betulaceae of high-alititude type move northerly and those of low-altitude type move easterly;3) the migratory way of the species is along the river,monutain and fault zone.