Abstract:Based on analysing the evolutionary polarities of 19 characters having important bearing on the phylogenetic relationships of the genus Ottelia, the present paper, by applying Wagner parsimony, dealt with the phylogenetic relationships among the 18 populations representing all the species of Ottelia so far known in China. A reasonable cladogram of the populations is constructed. The results suggest that the 18 populations could be classified into 4 groups corresponding to 4 taxonomic species. This is in conformity with the results of Q cluster analysis. The results indicate that cladistic analysis is not only as effective as Q cluster analysis in grouping taxa, but also could reveal the phylogenetic relationships of the taxa in question. Finally, the genus is postulated to originate in the areas of tropical lakies and swamps on Gondwanaland not later than Cretaceous period, and thereafter it evolves into three branches, i.e. polyovaries, submersed leaved-uniovary and floating leaved-uniovary branch, respectively.