Nomenclatural proliferation is defined and characterized as a phenomenon of explosive increase in the number of names within a taxon. The monophyletic genus Grusonia illustrates how the instability in the generic concept for this group of species has produced a disproportionate increase in names. This large increase in the number of names is due mainly to treatments presenting new combinations at the generic level without any significant reduction in the number of species through synonymy, and shows the uncoupling of the generation of new names from the publication of new species. Three historical nomenclatural phases in Grusonia are identified showing that the majority of the new names were proposed before any molecular phylogenetic reconstruction had an impact on the systematics of the group. However, molecular systematics has played an important role for the delimitation of a monophyletic genus. The lack of a solid phylogenetic hypothesis of relationships was one factor that promoted the superabundance of homotypic synonyms for these 17 species of North American grusonioids. In the face of this phenomenon, which we refer to as nomenclatural proliferation, the subgeneric categories in the subfamily Opuntioideae are historically devalued.