Abstract:Taxa of the Polygonum posumbucomplex, including P. posumbu, P. longisetum and its var. rotundatum, are taxonomically perplexing. By means of conventional taxonomic me-thods, it is difficult to discriminate them from one another. Basing upon herbarium materials of about 100 sheets of specimens collected from 11 provinces in China, a quantitative analysis of the correlations between certain key characters was thus made by applying the methods of pictorialized scatter diagram and histogram so as to reexamine the validity of the above taxa. Results from both methods have indicated that this complex could be divided into three parts: (1) Individuals-with branching repent stems without a central axis, blades usually ovate, ap-pressed hairy and with caudate tips, agreed well with typical P. posumbu; (2) Individuals-with more generally erect, stems, leaves lanceolate and usually glabrous, agreed with P. longisetum; (3) Individuals-characterized by angusti-lanceolate blades with truncate-round-ed or subcordate base, agreed with P. longisetum var. rotundatum. Both diagrams also showed that these three parts are so closely related to one another that they are by no means strictly seperable. Thus it is better to treat them all as varieties of the said complex.