Binomial nomenclature
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- For other topics using the name "binomial", see binomial (disambiguation).
In biology, binomial nomenclature refers to the formal method of 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 descriptor. Although the fine detail will differ, there are certain aspects which are universally adopted:
- Scientific names are usually printed in italics, e.g. Homo sapiens. When handwritten they should be underlined.
- The first term (genus name / generic name) is always capitalized, while the specific descriptor ("specific name" / "specific epithet") will not be. For example: Canis lupus or Felis silvestris.
- The scientific name should be written in full when it is first used or when several species from the same genus are being listed or discussed in the same paper or report. It may then be abbreviated by just using an initial for the genus; for example Canis lupus becomes C. lupus. 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.
- The abbreviation "sp." (or "spec.") is used when the actual specific name is not known: for example Canis sp. denotes "a species of the genus Canis". The abbreviation "spp." (plural) indicates "several unknown species".
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History
The adoption of a system of binomial nomenclature is due to Linnaeus who described the entire known natural world and gave every species (mineral, vegetable or animal) a two part name. However, binomial nomenclature in various forms existed before Linnaeus, and was used by the Bauhins, who lived nearly two hundred years before Linnaeus. Before Linnaeus hardly anybody used binomial nomenclature. After Linnaeus, almost everybody did.
Value of binomial nomenclature
The value of the binomial nomenclature system derives primarily from its economy and its widespread use:
- every species can be unambiguously identified with just two words;
- the same name is used all over the world, in all languages, avoiding difficulties of translation;
The procedures associated with establishing binomial nomenclature also 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 demoted from species to a lower rank, former species names may be retained as infraspecific descriptors.
Nomenclature 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 governing the naming of animals (ICZN), plants (incl. Fungi, cyanobacteria) (ICBN), bacteria (ICNB) and viruses.
These codes differ.
- For example, the ICBN, the plant Code does not allow tautonyms, whereas the ICZN, the animal Code does allow tautonymy.
- 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, in zoology in 1758. Bacteriology started anew, with a starting point in 1980[1]).
A BioCode has been suggested to replace several codes, although implementation is not in sight. There also is debate concerning development of a PhyloCode to name clades of phylogenetic trees, rather than taxa. Proponents of the PhyloCode use the name "Linnaean Codes" for the joint existing Codes and "Linnaean taxonomy" for the scientific classification that uses these existing Codes'.
Stability
The existing Nomenclature Codes aim (successfully) at stability of names. However, such stability as exists is far from absolute. A single organism may have several scientific names in circulation, depending on taxonomic point of view (see synonymy). Another source of instability is the resurrecting of forgotten names, which can claim priority of publication. In the latter case conservation according to the nomenclature Codes is possible.
Derivation of names
The genus name and species descriptor may come from any source whatsoever. Often they are Latin words, but they may also come from Ancient Greek, from a place, from a person (preferably a naturalist), a name from a 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 sentence. For this reason the name of a species is sometimes called its "Latin name," although this terminology is frowned upon by biologists, who prefer the phrase scientific name.
There is a separate list of Latin and Greek words commonly used in systematic names.
Extensions on the binomial name
Trinomial nomenclature of animals
In zoology, an animal species may be further subdivided, using trinominal 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, there are several ranks below that of species, notably subspecies, variety, and form. This is unlike zoology, where only one rank (subspecies) exists below that of species. Thus infraspecific names of plants must be accompanied by a qualifier (such as "subsp.") to indicate the rank, whereas trinomial names of animals are not. For example:
- Pinus nigra subsp. salzmannii
- Pinus nigra var. caramanica
An interspecific hybrid is designated with a multiplication sign before the epithet, e.g. Dianthus × allwoodii (Dianthus caryophyllus × Dianthus plumarius). An intergeneric cross is designated by a multiplication sign before the generic name, e.g. × Heucherella tirelloides (Heuchera sanguinea × Tiarella cordifolia) [2]. When a multiplication sign is not available (on a typewriter or in e-mail), a small letter "x" may be used instead.
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.
For example, in Pinus sylvestris L., the abbreviation "L." refers to Carolus Linnaeus; in 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 placed in parentheses and the author responsible for publishing the "move" is then appended. For example, 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.
For example, the Bowhead Whale was described and named by Carolus Linnaeus in his Systema Naturae of 1758, so it is cited as Balaena mysticetus Linnaeus, 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. For example, 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.
Footnote
- ^ 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.
- ^ The Language of Horticulture
