An electrophoretic survey of eight-enzyme loci in Riccia dictyospora detected three distinct sets of genotypes among 38 sampling localities representing the southeastern quarter of the United States. Mean genetic identity for populations representing a single genotypic set ranged from .hivin.I=0.856-0.939 while for populations representing different genotypic sets .hivin.I=0.211-0.454. The apparent inability of linkage to account for these genotypic sets and the frequent coexistence at individual collection localities of representatives of different genotypic sets suggest that R. dictyospora represents a composite of three sibling species.