Abstract: The present paper deals with a cladistic analysis of 15 species of the genus Populus using 23 characters (13 vegetative and 10 reproductive).Idesia, a genus of Flacourtiaceae, is adopted to be the outgroup based on recent data of angiosperm macrosystem as well as evidence of morphological characters. The characteristic polarities of the species of Populus involved are then determined by employing the recent common anesstor (ANC)-Idesia. The Wagner tree is constructed on the basis of parsimonious analysis. The result indicates that there are three evolutionary lines in the genus Populsu:the first is the most primitive Sect. Lence; the second, which includes Sect. Leucoides and Sect. Tacamahaca, is considered as the most variable one; and the third includes the most advanced Sect. Aigeiros and Sect. Aigeiros and Sect. Turanga. A close relationship between Sect. Leuce and Sect. Leucoides is recognized. Sect. Turanga is the most advanced one in Populus. The morphological variation and geographic distribution of Sect. Tacarrahaca in China are discussed.