Untergattung

Untergattung, in taxonomy often referred to as subgenus, is a rank between genus and species. It serves to organize species within a genus into smaller, closely related groups when the genus is diverse or contains lineages that merit separate treatment without creating new genera. The use of Untergattung is not mandatory; some genera are divided into subgenera, while others are left undivided and described only at the genus and species levels. In modern practice, subgenera are chosen to reflect phylogenetic relationships or distinctive morphological, ecological, or geographic features.

In zoology, the subgenus is a formal rank, and its name is typically written in parentheses after the genus name when a species is cited with subgeneric placement. For example, Drosophila (Sophophora) melanogaster or Rattus (Rattus) norvegicus. In botany, the rank is also widely used, with a standard notation such as Genus subgenus epithet, often written as Genus (Subgenus) species. The subgenus name is capitalized and the species epithet is lower-case, with the entire binomial typically set in italics.

Etymology derives from German Untergattung meaning “under genus.” The concept dates back to the Linnaean framework and was developed further in the 19th and 20th centuries as classifications grew more detailed. Today, Untergattung remains a useful but optional tool in taxonomic practice, complementing genera and species with a finer hierarchy to clarify evolutionary relationships. See also genus, species, taxonomy, and nomenclature.