Abstract:Based on stereomicroscopic and scanning electronic microscopic observation, we studied the hair morphology and distribution on leaf of 34 species of Astragalus Sect. Trachycersis Bunge from China in order to identify their variation pattern and taxonomic significance. The results showed that hairs are distributed on both upper and lower leaf surfaces of all studied species except for A. galactites, in which hairs are only on lower surface of leaves. The distribution, morphology, length and arm ratio of hairs are varied in different species. Haris are medifixied, hollow, appressed or spreading, densely to sparsely papillose on hair surfaces. Among them, appressed hairs are inflated on base of attachment, gradually thinner from middle to both ends, while spreading ones generally are slender filiform or linear, smooth or with striation. In our point, those appressed, short and straight, smooth with densely papillose, and with small arm ratio, flat hairs are ancestral characters, while those spreading, long and dense, filiform or linear, with striate ornamentation and sparsely papillose on surface, and with big arm ratio are advanced ones. On the basis, we discussed taxonomy of some related species in this section.