In taxonomy, binomial nomenclature ("two-term naming system"), also called binominal nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomial name (which may be shortened to just "binomial"), a binomen, binominal name or a scientific name; more informally it is also historically called a Latin name.
The first part of the name – the generic name – identifies the genus to which the species belongs, whereas the second part – the specific name or specific epithet – distinguishes the species within the genus. For example, modern humans belong to the genus Homo and within this genus to the species Homo sapiens. Tyrannosaurus rex is likely the most widely known binomial. The formal introduction of this system of naming species is credited to Carl Linnaeus, effectively beginning with his work Species Plantarum in 1753. But as early as 1622, Gaspard Bauhin introduced in his book Pinax theatri botanici (English, Illustrated exposition of plants) many names of genera that were later adopted by Linnaeus.
The application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature (ICZN) for animals and the International Code of Nomenclature for algae, fungi, and plants (ICNafp). Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences, both in terminology they use and in their particular rules.
In modern usage, the first letter of the generic name is always capitalized in writing, while that of the specific epithet is not, even when derived from a proper noun such as the name of a person or place. Similarly, both parts are italicized in normal text (or underlined in handwriting). Thus the binomial name of the annual phlox (named after botanist Thomas Drummond) is now written as Phlox drummondii. Often, after a species name is introduced in a text, the generic name is abbreviated to the first letter in subsequent mentions (e. g., P. drummondii).
In scientific works, the authority for a binomial name is usually given, at least when it is first mentioned, and the year of publication may be specified.
- In zoology
- "Patella vulgata Linnaeus, 1758". The name "Linnaeus" tells the reader who published the name and description for this species; 1758 is the year the name and original description was published (in this case, in the 10th edition of the book Systema Naturae).
- "Passer domesticus (Linnaeus, 1758)". The original name given by Linnaeus was Fringilla domestica; the parentheses indicate that the species is now placed in a different genus. The ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs usually include such information.
- In botany
- "Amaranthus retroflexus L." – "L." is the standard abbreviation used for "Linnaeus".
- "Hyacinthoides italica (L.) Rothm." – Linnaeus first named this bluebell species Scilla italica; Rothmaler transferred it to the genus Hyacinthoides; the ICNafp does not require that the dates of either publication be specified.