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- For other topics using the name "binomial", see binomial (disambiguation).
In biology, binomial nomenclature is a standard convention used for naming species. As the word 'binomial' suggests, the scientific name of a species is formed by the combination of two terms: the genus name and the species epithet or descriptor. The first term (generic name) is always capitalized, while the specific epithet (trivial "name") is not; both are to be typeset in italics, e.g. Homo sapiens. The genus name can be abbreviated to its initial letter, but never omitted, (as H. sapiens) when repeated or when several species from the same genus are being listed or discussed in the same paper or report. In rare cases this abbreviation form has spread to more general use—for example the bacterium, Escherichia coli, is often referred to as just E. coli.
Origin of names
The species descriptor should be an adjective that differentiates a species from other members of a genus. The genus name and species descriptor are usually derived from Latin, although Latin derivation is not universal. Names sometimes come from Ancient Greek, or from local languages, or from the name of the person who first discovered the species. In fact, taxonomists come up with species names from a variety of sources, including in-jokes and puns. However, 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," although this terminology is frowned upon by biologists. The term scientific name, however, is considered acceptable. There is a separate list of Latin and Greek words commonly used in systematic names.
Value and use of the binomial system
The value of the binomial system derives primarily from its economy and its widespread use:
- the same name is used in all languages, avoiding difficulties of translation;
- 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 1980).
The procedures associated with establishing binomial nomenclature tend to favor stability. In particular, 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 found to belong to the same species, former species names may be retained as subspecies terms.
However, such stability as exists is far from 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.
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 concerning development of a PhyloCode to name clades of phylogenetic trees.
Extensions on the binomial name
Trinomial nomenclature of animals
In zoology, an animal species may be further subdivided, using trinomial nomenclature to indicate a subspecies (sometimes called a race), e.g. the Great Cormorants (Phalacrocorax carbo) found in New Zealand differ slightly from those found elsewhere, and are classified as the subspecies Phalacrocorax carbo novaehollandiae. Only the single infraspecific rank is ever used in zoology, so no additional indication of rank is required, with the third place position sufficient to indicate it is a subspecies.
Botanical subdivision of species
In botany, a species can be further divided into any of subspecies, variety, or form, unlike zoology where a species is only subdivided into subspecies. Infraspecific names of plants therefore must include a qualifier (such as "subsp.") to indicate the rank used, whereas trinomial names of animals never do. A single plant species may have subpsecies (e.g. Pinus nigra subsp. salzmannii), varieties (e.g. Pinus nigra var. caramanica), and varieites of subspecies (e.g. Pinus nigra subsp. salzmannii var. corsicana), or even more complex terminology.
Authorship in scientific names
Sometimes you will see a name or abbreviation of a name after a scientific name and even a year as well. A complete reference to a species includes not only the binomial name, but also the author(s) that described the species and gave it a name. While the scientific name is italicized, the author citation is not. This addition of authorship is usually only done once in a particular article or citation. Conventions in author citation differ somewhat between botany (plants) and zoology (animals), and are governed by the International Code of Botanical Nomenclature and International Code of Zoological Nomenclature respectively.
Botanical author citation
The name or names of plant authors are abbreviated to a standardised index of author names published by the Royal Botanic Gardens, Kew; the date of publication is not cited in brief citations. The standard abbreviations can be found at the International Plant Names Index, Author Query page.
Thus, in e.g. Pinus sylvestris L., the abbreviation "L." refers to Carolus Linnaeus; in e.g. Pinus koraiensis Siebold & Zucc., Siebold refers to Philipp Franz von Siebold and Zucc. refers to the co-author Joseph Gerhard Zuccarini.
If at some point, a species is moved into a different genus, the original author is put in parentheses and the author responsible for publishing the "move" is then appended. Thus e.g. the Coast Redwood was first described by David Don, as Taxodium sempervirens D. Don. Subsequently, Stephan Ladislaus Endlicher pointed out that it was dissimilar to the other species of Taxodium, and transferred it to a new genus, publishing the combination Sequoia sempervirens (D. Don) Endl..
In articles concerning the detailed listing or taxonomy of a plant, the date and place of publication associated with the authorship is added as well, but this practice is rare in encyclopedic or other non-taxonomic works. In the above example the full citation is Sequoia sempervirens (D. Don) Endl., Syn. Conif. 198 (1847), referring to page 198 of Endlicher's Synopsis Coniferarum, published in 1847.
Zoological author citation
The name or names of animal authors have their surname given in full, not abbreviated, while first names are not included, or if two authors share the same surname, are given as initials. The date of first publication is also cited, with a comma between the author and date.
Thus, in e.g. Balaena mysticetus Linnaeus, 1758, also described by Carolus Linnaeus, Linnaeus' surname is given in full, and followed by the date of publication 1758.
If a species is later transferred to a different genus, the original author and date are given in brackets to show that a revision has been made, but the revising author and date of revision are not cited. Thus e.g. the White-fronted Goose was first described by Giovanni Antonio Scopoli, as Branta albifrons Scopoli, 1769. It was later shown to be more closely related to the grey geese in the genus Anser than to the black geese in Branta, so it was transferred to that genus and is now cited as Anser albifrons (Scopoli, 1769).
Here too in formal taxonomic publications, a fuller citation is given, citing the original name and publication, in this case as Branta albifrons Scopoli, 1769, Annus I Hist.-Nat. 69.
Carolus Linnaeus invented the idea of organizing species within a hierarchical classification based upon shared characteristics, a system closely associated with binomial nomenclature. It is a common misconception that Linnaeus also invented binomial nomenclature; in fact it dates back to the Bauhins, who lived nearly 200 years before Linnaeus. He was, however, the first to systematize and popularize binomial nomenclature, and it is only one aspect of his systematical achievements or misachievements (such as oversimplifying fungal systematics).
- The botanical code kept references to bacteria until 1975. A bacteriological code of nomenclature was approved at the 4th International Congress for Microbiology in 1947, but was later discarded. The official "Nomenclatural Starting Date" for the current International Code for bacteria is January 1, 1980.