Mentha is a member of the tribe Mentheae in the subfamily Nepetoideae. The tribe contains about 65 genera, and relationships within it remain obscure. Authors have disagreed on the circumscription of Mentha. For example, M. cervina has been placed in Pulegium and Preslia, and M. cunninghamii has been placed in Micromeria. In 2004, a molecular phylogenetic study indicated that both M. cervina and M. cunninghamii should be included in Mentha. However, M. cunninghamii was excluded in a 2007 treatment of the genus.
More than 3,000 names have been published in the genus Mentha, at ranks from species to forms, the majority of which are regarded as synonyms or illegitimate names. The taxonomy of the genus is made difficult because many species hybridize readily, or are themselves derived from possibly ancient hybridization events. Seeds from hybrids give rise to variable offspring, which may spread through vegetative propagation. The variability has led to what has been described as “paroxysms of species and subspecific taxa”; for example, one taxonomist published 434 new mint taxa for central Europe alone between 1911 and 1916. Recent sources recognize between 18 and 24 species.