the genus was first described by carl linnaeus in 1753. within the family polygonaceae, it is placed in the subfamily polygonoideae. the genus "emex" was separated from "rumex" by francisco campderá in 1819 on the basis that it was polygamous (i.e. had both bisexual and unisexual flowers on the same plant). however, some species of "rumex" subg. "acetosa" also have this characteristic, and most other features that are supposed to distinguish "emex" are found in species of "rumex". accordingly, in 2015, schuster et al. demoted "emex" to a subgenus of "rumex".