At least some of the species of the genus Caltha are polymorphic, showing not only a wide range of intraspecific morphological variation, but also considerable cytotaxonomic differentiation. A number of taxonomic problems are connected with this phenomenon. In a previous paper (Smit, 1967) a survey of the chromosome numbers of 46 Dutch populations was given. Two cytotypes of Caltha palustris were found, 2n = 32 and 2n = 56, respectively, with slight morphological differences and different ecological preferences.