|| Three species of Cyperaceous weeds, Cyperus iria (12 strains), C. microiria(12 strains) and C. amuricus (6 strains), were collected from different sites of Okayama, Tottori and Tokyo prefectures, and various morphological characters, biomass and seed production were observed on the plants which were cultivated at Kurashiki. The analysis of variance showed a significant difference among the strains in each character. However, the species overlapped with each other in most morphological characters. Prinipal component analysis on the 21 characters showed that 83% of the total variation could be explained by the first three components: the first component (37%) was regarded as factors concerning spikelet and seed production; the second component (28%) was regarded as factors concerned the size of vegetative parts; the third component (18%) was largely affected by seed weight and floret density. Scatter diagram on the first and third principal components showed that the 30 strains of three species divided into three groups, and strains in each group correspond to the three species without exception. Based on the second and third principal components, strains of C. microiria were further divided into three sub-groups according to size of vegetative parts. Using the cluster analysis, 30 strains of these species were divided into four large clusters; the first was composed of C. amuricus strains, the second was of three strains of C. microiria, the third included the remaining strains of C. microiria, and the last cluster was composed of C. iria strains. It may be concluded that C. microiria is composed of two or three ecotypes which are different in morphological and reproductive traits.