Contrary to Europe, with only one Caltha species, North America has at least three species of this genus. These are the polymorphic C. palustris L., also widely distributed in Europe, the floating aquatic C. natans Pall, and the polymorphic C. leptosepala-biflora group. Two previous papers (Smit 1967, 1968) dealt with taxonomic aspects of C. palustris, that in North America were not essentially different from those of European material.