Abstract: On the Principles and methods of cladistics, the phylogenetic relationships in Roegneria of Poaceae were analysed in the present paper. Eighteen series of Roegneria in traditional taxonomy were recognized and regarded as the terminal taxa, and its twenty-three characters from morphology, anatomy, cytology and palynology were selected as the basis for constructing data matrix. Brachypodium of the tribe Bromeae was chosen as an outgroup, and used for determining polarities of external characters;the data of characters analysed in the past were used for judging the polarities of microcosmic characters. The data matrix was computed with the PAUP program. Six equally parsimonious cladograms were obtained and the one with the lowest f-value of 0.228 was selected as base for making cladistic analysis. The results of analysis show that the sections or series revealed by the cladogram basically agree with those in traditional taxonomy, and the phylogenetic relationships among the taxa are also consistent those inferred by a unilateral evidence in the past. In the cladogram, however, the taxa of Sect. Goulardia were not derived from a identical ancestor, and the section probably possesses a complex composition;the systematic positions of one or two series are different from those of the series analysed by the macroscopic characters.

Key words: Roegneria, cladistics, phylogeny