A genus (/, pl. genera) is a
taxonomic rank used in the
biological classification of
biology. In the hierarchy of biological classification, genus comes above
species and below
binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.
Felis catus and
Felis silvestris are two species within the genus
Felis. Felis is a genus within the family
The composition of a genus is determined by a
taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however,
 including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:
monophyly – all descendants of an ancestral
taxon are grouped together (i.e. phylogenetic analysis should clearly demonstrate both monophyly and validity as a separate lineage
- reasonable compactness – a genus should not be expanded needlessly; and
- distinctness – with respect to evolutionarily relevant criteria, i.e.
DNA sequences are a consequence rather than a condition of diverging evolutionary lineages except in cases where they directly
gene flow (e.g.
Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.