Study on the Floristic Characteristics in Longwu River Valley

There are 970 species,329 genera,65 families of seed plants distributed in this area (34°50′-35°55′N and 100°40′-102°30′E).Its floristic characteristics are as follows:(1)The flora is formed under the influence of alpine arctic and xeric ecological environment.(2)The floristic composition consists mainly of perennial herbs only accompanied with few trees and annuals.(3)The north temperate elements are superior than the old world temperate elements and others in numbers.(4)The flora belongs to young and derivative.(5)The endemic species coincide with some of those distributed in SW,NW and N China.(6)The flora is situated in the area with a transitional habitat for species differentiation,viz.the flora is influenced by the transitional area effect.By analyzing the floristic composition abounded with alpine and xeric elements,it is clear that the flora belongs to the Qinghai Tibet plateau flora and closely related to those of Hangduan mountains and S Gansu.It is suggested that the boundary of the Tangute Region of flora slauld be redefined based upon the further study of the flora existed in this area and its adjacent areas.