Abstract: 1. Having analyzed the external morphology of the genus Microula, the author has proposed a series of criteria as bases for the construction of a classification scheme of this genus. The most important ones are as follows: 1) The normally developed stem is primitive, and the strongly abbreviated stem more advanced. 2) The small inconspicuous bracts are more primitive than the large suborbicular densely arranged ones, which almost entirely cover the flowers and the fruits. 3) Nutlets with small dorsal pit are more primitive than those with larger pit on one hand or those without it on the other. 4) The dorsal pit with simple margin precedes that with double margins. 5) Nutlets with subbasal areola precede those with lateral or apical areola. 6) Nutlets without glochids precede those with glochids. 2. Basing upon these criteria the genus Microula may be divided into six sections. The section Schistocaryum may be the primitive one, and the others may be evolved from it respectively. The possible affinities between them are demonstrated in figure no. two. 3. The genus Microula, containing 30 species, is mainly distributed in the Chinghai-Tibetan plateau and the majority of its species concentrates in the eastern border of the plateau, and of the 30 species 26—that is 90 percent—are endemic to China, and the remaining 4 are distributed elsewhere in China, too, and extending southward and westward to Bhutan, Sikkim, Nepal and Kashmir respectively. In the region between Heishui, Province Szechuan, and Chinghai Lake there are 9 species, which, curiously, represent all the six sections of Microula, hence this region seems to be the center of maximum variation of this genus. M. ovalifolia whose nutlets have small dorsal pit and subbasal areola may be considered the most primitive species. Thus the author is of the opinion that the western part of province Szechuan, to which M. ovalifolia is endemic, may probably be the center of origin of the genusMicroula.