The fundamental unit of classification for all organisms is the species. Species names are made up of two parts: the generic name and the specific name. The generic part indicates the species' relationship to other species within the same genus.. A species forms the basal unit of a taxonomic hierarchy that has a number of higher ranks - genera, families and orders.
Example: Atropa belladonna from which the homeopathic remedy Belladonna is prepared is the species belonging in the genus Atropa in the family Solanaceae in the order Solanales.
Early names for plants were simple nouns with adjectives added to distinguish between species and other taxonomic groups. The noun gradually took on the role of the generic name and adjectives became the specific epithets.
Linnaeus the Swedish naturalist created the binomial system that we use today. He assigned a generic and a specific epithet to more than 9000 plant species in his Species Plantarum (Linnaeus, 1753).
The International Code for Botanical Nomenclature (ICBN) became essential as more plants were discovered and described, because the same species is sometimes named more than once by different botanists. Each species can have only one name and the first validly published name takes precedence over later names. All other names are reduced to synonymy.