Linnaeus was the first to develop a system, based on flower parts, of using two names, one for genus and one for species, for naming plants and animals. The genus is a classification of plants or animals that are similar by virtue of having common distinguishing characteristics. Each member is closely related to other species in the same genus. The genus is the main subdivision of a family of plants. While the family name is not included in the binomial, it is helpful to think of a given species in terms of the family to which it belongs, those plants sharing characteristics that are common to all genera in the same family.
Some families are very large and contain many genera.
Both family and genus may be monotypic. The genus name, the first name in the binomial, is always capitalized. The second name, the species name, is never capitalized, even when it is a proper name. The binomial is always underlined. Once a name is assigned, no other species may be assigned that name.