In order to investigate phylogenetic relationships between diploid and triploid taros, Colocasia esculenta (L.) Schott, 13 enzyme systems were analyzed for isozyme variations using 59 accessions collected in Nepal and Yunnan Province of China. A total of 115 banding positions were discovered, which successfully differentiated most of the accessions. Isozyme bands specific to triploids were observed only at five out of 115 positions, indicating autopolyploid origin of the triploids: almost all isozyme variations in triploids are derived from those in diploids. The Wagner parsimony method, applied to the band presence or absence data of 59 accessions, determined 65 most parsimonious trees. These trees contain consistent relationships among most of the Nepal and some of the Yunnan accessions; entire accessions are clearly divided into two geographical groups, and diploids and triploids tend to form separate groups in each geographical group. Triploid taros are believed to arise from diploids by fertilization of an unreduced gamete with a normal gamete. Unreduced gamete formation can occur repeatedly in any environment, but the triploid taros are generally found in marginal environments. Based on this evidence, it is concluded that geographical differentiation proceeded between Nepal and Yunnan, and triploids were formed and established as adapted plants in each area.