A genus is a category of biological classification that ranks between the family and the species, and consists of related species that share common characteristics. The genus name is the first word of a binomial scientific name, and is always capitalized. For example, the genus name of the rose plant is Rosa, which contains more than 100 species of roses.
A plant genus is a taxonomic group that unites closely related plant species that have a common ancestor. Plant genera are often named after their most distinctive or representative species, or after the person who discovered or described them. For example, the plant genus Ginkgo is named after its only living species, Ginkgo biloba, which is also called the maidenhair tree.