A genus (,  genera) is a taxonomic rank used in the biological classification of living and fossil organisms in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus. 

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: 

Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera. 

The term comes from the Latin ' ("origin; type; group; race"), a noun form cognate with ' ("to bear; to give birth to"). Linnaeus popularized its use in his 1753 "Species Plantarum", but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera". 

The scientific name of a genus may be called the generic name or generic epithet: it is always capitalized. It plays a pivotal role in binomial nomenclature, the system of naming organisms.
What should genera be composed of?
Moreover, genera should be composed of phylogenetic units 