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Binomial nomenclature (also called binominal nomenclature 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 are based in some way on the Latin language. Such a name is called a binomial name (which may be shortened to just "binomial"), a binomen or a scientific name; more informally it is also called a Latin name. The first part of the name identifies the genus to which the species belongs; the second part identifies the species within the genus. For example, humans belong to genus Homo and within this genus to the species Homo sapiens. The introduction of this system of naming species is usually credited to Linnaeus.

The application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are International Code of Zoological Nomenclature for animals and the International Code of Botanical Nomenclature for plants. Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences in the terminology they use and their precise rules. For example:

• "Binomial nomenclature" is the correct term for botany,^[1] although it is also used by zoologists.^[2] Since 1953, "binominal nomenclature" is the technically correct term in zoology.^[3]
• Both codes agree in calling the first part of the two-part name for a species the "genus name". However in zoological nomenclature the second part is called the "species name", whereas in botanical nomenclature the second part is called the "species epithet", and the term "species name" should only be used for the whole name, i.e. the combination of the two parts.

The first letter of the first name, the genus, is always capitalized, while that of the second is not, even when derived from a proper noun such as the name of a person or place. Conventionally, all names of genera and lower taxa are always italicised, while family names and higher taxa are printed in plain text. Species can be divided into a further rank, giving rise to a trinomial name for a subspecies (trinomen for animals, infraspecific name for plants).

Biologists, when using a name of a species, usually also give the authority and date of the species description. Thus zoologists will give the name of a particular sea snail species as: Patella vulgata Linnaeus, 1758. The name "Linnaeus" tells the reader who it was that described the species; 1758 is the date of the publication in which the original description can be found, in this case the book Systema Naturae.

History

The adoption by biologists of a system of binomial nomenclature is due to Swedish botanist and physician Carl von Linné, also known by his Latinized name Carolus Linnaeus (1707–1778). Linnaeus attempted to describe the entire known natural world. He chose a convenient short-hand binomial scheme for species, using only the genus name and the specific name or specific epithet (the terms now used in zoology and botany respectively). Together these form the whole name of the species. Linnaeus attempted to give every species (mineral, plant, or animal) a two-part name. This was an improvement over descriptive names that involved a whole descriptive phrase comprising numerous words. However, binomial nomenclature in various forms had existed before Linnaeus, and was used by the Bauhins, who lived nearly two hundred years earlier.^{[citation needed]}

Value

The value of the binomial nomenclature system derives primarily from its economy, its widespread use, and the stability of names it generally favors:

• Clarity. It avoids the confusions that can be created when attempting to use common names to refer to a species. Common names often differ even from one part of a country to another part, and certainly vary from one country to another. In contrast, the scientific name can be used all over the world, in all languages, avoiding confusion and difficulties of translation.
• Stability. The procedures associated with establishing binomial nomenclature tend to favor stability. Even though such stability as exists is far from absolute, it is still advantageous. For example, when species are transferred between genera (as not uncommonly happens as a result of new knowledge), if possible the species descriptor is kept the same. Similarly if what were previously thought to be distinct species are demoted from species to a lower rank, former species names may be retained as infraspecific descriptors.

Despite the rules favoring stability and uniqueness, in practice a single species may have several scientific names in circulation, depending largely on taxonomic point of view (see synonymy).

Derivation

The two-part name of a species is also commonly known as its Latin name, since every two-part scientific name is either formed out of (modern scientific) Latin or is a Latinized version of words from other languages. However, biologists and philologists prefer to use the term scientific name rather than "Latin name", because the words used to create these names are not always from the Latin language, even though words from other languages have usually been Latinized in order to make them suitable for this purpose. Species names are often derived from Ancient Greek words, or words from numerous other languages. Frequently species names are based on the surname of a person, such as a well-regarded scientist, or are a Latinized version of a relevant place name.

The genus name and specific descriptor may come from any source. Often they are ordinary New Latin words, but they may also come from Ancient Greek, from a place, from a person (often a naturalist), a name from the local language etc. In fact, taxonomists come up with specific descriptors from a variety of sources, including in-jokes and puns. However, names are always treated grammatically as if they were a Latin phrase.

Genus name

The genus name or generic epithet must be unique inside each kingdom. It is the nominative singular form of a noun or an adjective treated as a noun in Latin grammar.

Family names are often derived from a common genus within the family.

Species name

The species name or specific epithet is also a Latin word, but it can be one of various grammatical forms, including the following:

• A nominative form:
  • of a noun, in apposition with the genus, for example, the lion Panthera leo. The two nouns do not have to agree in gender: in this case, Panthera is feminine and leo is masculine.
  • of an adjective, modifying the genus name, as in the house sparrow Passer domesticus. Here domesticus ("domestic") simply means "associated with the house". The adjective must agree in gender with the genus name. Thus the sacred bamboo is Nandina domestica rather than Nandina domesticus, since Nandina is feminine whereas Passer is masculine. The tropical fruit langsat is derived from Lansium domesticum, since Lansium is neuter.
• A genitive (possessive) form:
  • of a person's surname, as in the Tibetan antelope Pantholops hodgsonii, the shrub Magnolia hodgsonii, or the Olive-backed Pipit Anthus hodgsoni. Here, the person named is not usually (if ever) the person who names the species; for example Anthus hodgsoni was named by Charles Wallace Richmond, in honour of Hodgson.
  • of a place name, as with Latimeria chalumnae ("of the Chalumna River")
  • of a common noun (singular or plural), as in the bacterium Escherichia coli. This is common in parasites, as in Xenos vesparum where vesparum simply means "of the wasps"

The same specific name or epithet is quite commonly used in two or more different genera (as is shown by examples of hodgsonii above).

Codes

From the mid nineteenth century onwards it became ever more apparent that a body of rules was necessary to govern scientific names. In the course of time these became nomenclature codes. The International Code of Zoological Nomenclature (ICZN) governs the naming of animals, the International Code of Botanical Nomenclature (ICBN) that of plants (including fungi and cyanobacteria), and the International Code of Nomenclature of Bacteria (ICNB)that of bacteria (including Archaea). Virus names are governed by the International Committee on Taxonomy of Viruses (ICTV), a taxonomic code, which determines taxa as well as names. These codes differ in certain ways, e.g.:

• The ICBN, the plant Code, does not allow tautonyms, whereas the ICZN, the animal Code, does.
• The starting points, the time from which these codes are in effect (retroactively), vary from group to group.
  • In botany the starting point will often be in 1753 (the year Carl Linnaeus first published Species Plantarum).
  • In zoology the starting point is 1758 (1 January 1758 is considered the date of the publication of Linnaeus's Systema Naturae, 10th Edition, and also Clerck's Aranei Svecici).
  • Bacteriology started anew, with a starting point on 1 January 1980.^[4]

A BioCode has been suggested to replace several codes, although implementation is not in sight. There is also a code in development for naming clades, called the PhyloCode.

Rules

Although the fine detail differs, there are certain aspects which are universally adopted:

• As the words "binomial", "binominal" and "binary" all signify, the scientific name of each species is formed by the combination of two words, which are in a modern form of Latin:
  1. the genus name (also called the generic name).
  2. a second word identifying the species within that genus, for which the technical term varies, as follows:
     • a general term for the word identifying the species is the specific descriptor
     • in zoology, the word identifying the species is called the specific name
     • in botany, the word identifying the species is called the specific epithet
• Species names are usually typeset in italics; for example, Homo sapiens. Generally the binomial should be printed in a font different from that used in the normal text; for example, "Several more Homo sapiens were discovered." When handwritten, they should be underlined; for example, Homo sapiens. Each name should be underlined individually.
• The genus name is always written with an initial capital letter.
• In current usage, the species name is never written with an initial capital.^[5][6]

For example, the entire tiger species is Panthera tigris

• Some older works, on the other hand, wrote some specific names (epithets) with an initial capital, principally those derived from proper nouns, e.g. Berberis Darwinii^[7]
• There are several terms for this two-part species name; these include binomen (plural binomina), binomial <name>, binominal <name>, and species name.
• All taxa at ranks above species have a name composed of one word only, a "uninominal name".
• The first level subdivisions within a species, termed subspecies, are each given a name with three parts: these are the two forming the species name, plus a third part (the subspecific name) which identifies the subspecies within the species. This is called trinomial nomenclature, and is written differently in zoology and botany.^[8] For example:
  • Two of the subspecies of Olive-backed Pipit are Anthus hodgsoni berezowskii and Anthus hodgsoni hodgsoni
  • The Bengal tiger is Panthera tigris tigris and the Siberian tiger Panthera tigris altaica
  • The tree European Elder is Sambucus nigra subsp. nigra and the American Black Elder is Sambucus nigra subsp. canadensis
• In scholarly texts, the main entry for the binomial is followed by the abbreviated (in botany) or full (in zoology) surname of the scientific authority – the scientist who first published the classification. If in the original description the species was assigned to a different genus from that to which it is assigned today, the abbreviation or name of the describer and the description date are set in parentheses.

For example: (plant) Amaranthus retroflexus L., and (animal) Passer domesticus (Linnaeus, 1758) – the latter was described by Linnaeus as Fringilla domestica.

• When used with a common name, the scientific name often follows in parentheses, although this varies with publication.

For example: "The house sparrow (Passer domesticus) is decreasing in Europe".

• The scientific name should generally be written in full. The exception to this is when several species from the same genus are being listed or discussed in the same paper or report, or the same species is mentioned repeatedly; in that case the genus is written in full when it is first used, but may then be abbreviated to an initial (and period) for successive species names; for example, a list of members of the genus Canis might be written: "Canis lupus, C. aureus, C. simensis". In rare cases, this abbreviated form has spread to more general use; for example, the bacterium Escherichia coli is often referred to as just E. coli, and Tyrannosaurus rex is perhaps even better known simply as T. rex, these two both often appearing in this form even where they are not part of any list of species of the same genus.
• The abbreviation "sp." is used when the actual specific name cannot or need not be specified. The abbreviation "spp." (plural) indicates "several species". These are not italicised (or underlined).

For example: "Canis sp." means "an unspecified species of the genus Canis", while "Canis spp." means "two or more species of the genus Canis".

• Easily confused with the foregoing usage is the abbreviation "ssp." (zoology) or "subsp." (botany), indicating an unspecified subspecies (see also trinomen, infraspecific name (botany)). In the same way the plurals of these are "sspp." or "subspp."
• The abbreviation "cf." is used when the identification is not confirmed.

For example "Corvus cf. splendens" indicates "a bird similar to the House Crow but not certainly identified as this species".

• Mycology uses the same system as in botany.

See also

• Botanical name (in botany)
• Hybrid name
• List of botanists by author abbreviation
• List of zoologists by author abbreviation
• Species description

References

External links

• Curiosities of Biological Nomenclature
• The Language of Horticulture