Abstract: Because of its special feature of morphology, the phylogenetic status of Potaninia is still argued today.The ITS sequences of six species of Rosoideae and a species of Prunoideae are obtained in the study. The other five ITS sequences of five species of Rosaceae are gotten from Genbank and analyzed together. The result of comparing ITS1+ITS2 sequences of 12 plants shows that the sizes of sequences of different plants are different greatly. The sequences of ITS1 range from 224~266 bp. The sequences of ITS2 range from 202~221 bp. The result of phylogenetic analysis with PAUP 3.1.1 shows that Dasiphora is the closest genus with Potaninia;the second is Chamaerhodos;the third is Sibbaldia. The mutual feature of the three genera is that style grows from the end or side of ovary. Traditionally, Potaninia is arranged near Rosa and Agrimonia judged by torus like chalis or jar, which is not consistent with our result. The phylogenetic tree indicates that Prunus mongolica and Prunus cerasifera form a monophiletic taxa obviously, which show the relationship of Potaninia mongolica and Prunus mongolica is very far. The study also indicate Potaninia mongolica, a axerophilous floristic element of Mongolian Plateau, is derived from D.glabra, a mesophytic floristic element of East Asia;All morphological characteristics and ecological habit are the result adapting itself to dry climate of desert for ages. The discovery of derivation and migrating route provide the new proof for studying the formation of desert flora and vegetation of midst of Asia.

Key words: Potaninia, Rosoideae, ITS, Phylogenetic status