In biology, binomial nomenclature is a standard convention used for naming species. As the word 'binomial' suggests, the scientific name of each species is the combination of two names: the genus name and the species epithet. The name of the genus (generic name) is always capitalized, while the specific epithet (trivial name) is not; both are usually typeset in italics, e.g. Homo sapiens. The genus name is usually abbreviated to its initial letter when several species from the same genus are being listed, or discussed in a single paragraph; in a few cases this abbreviation has spread to more general use - for example the bacterium Escherichia coli is usually referred to as E. coli.
The names used are usually derived from Latin. Although Latin derivation is not universal (names sometimes come from Ancient Greek, sometimes from local languages, and often from the name of the person who first described a species), the names are always treated grammatically as if they were Latin words. For this reason the binomial name of a species is sometimes called its "Latin name", though this usage is frowned on by biologists. The term "Scientific name" is more acceptable. There is a separate list of Latin and Greek words commonly used in systematic names.
When a species is further divided, a Trinomial nomenclature is used (e.g. Astrophytum myriostigma subvar. glabrum). A species can be further divided into any of subspecies, variety, subvariety or form.
The value of the binomial system derives primarily from its economy and its widespread use:
- every species can be unambiguously identified with just two words;
- the system has been adopted internationally in botany (since 1753), zoology (since 1758) and bacteriology (since 1980¹).
However, such stability as exists is far from being absolute. A single organism may have several scientific names in circulation, depending on opinion (see synonymy), conservation according to nomenclature codes, and new findings based on molecular phylogeny. Another source of instability is the rule that nomenclature should respect priority of discovery.
The binomial name of a species, of course, only reflects part of the larger classification of the organism:
Carolus Linnaeus invented this classification, but it is a common misconception that he also invented binomial nomenclature; in fact it dates back to the Bauhins. Linnaeus, however, was the first to systematize and popularize it, and it is only one aspect of his systematical achievements or misachievements (such as oversimplifying fungal systematics).
Binomial nomenclature is only one of many conventions used to name organisms. Nomenclature codes rule the naming of plants (incl. Fungi, cyanobacteria) / cultivated plants / animals / bacteria / viruses. These codes differ. For example, the ICBN plant nomenclature does not allow tautonymy, whereas the ICZN animal code allows it. A BioCode has been suggested to replace several codes, but there also is debate of a PhyloCode to name clades of phylogenetic trees.
For more information on this system, please see scientific classification and numerical taxonomy.