Binomial nomenclature

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.

Origin of names

The names used are usually derived from Latin. Although Latin derivation is not universal (names sometimes come from Ancient Greek, sometimes from local languages, often from the name of the person who first described a species) and sometimes in a playful way, such as a pun, 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.

Value 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 1980¹).

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), wherever possible species names are kept the same. Similarly if what were previously thought to be distinct species are found to belong to a single species, former species names are when applicable retained as a lower taxon name.

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.

Extending the binomial name

Trinomial nomenclature

When a species is further divided, a trinomial nomenclature is used, e.g. Astrophytum myriostigma subvar. glabrum.

In botany, a species can be further divided into any of subspecies, variety, subvariety or form, whereas in zoology, a species is only subdivided into subspecies. Trinomial names of plants therefore usually include a qualifier (such as "subvar." in the example above), whereas trinomial names of animals never do. For example, Phalacrocorax carbo novaehollandiae is the Black Shag, the subspecies of the Great Cormorant found in Australia and New Zealand, and there is no need to indicate explicitly that novaehollandiae is a subspecies name.

Authorship in scientific names

Sometimes you will see a name or abbreviation after a scientific name, sometimes including a date, generally at the top of a page. An official reference to a species includes not only the genus and species, but the author(s) of the name. This is usually abbreviated if possible, e.g. Urtica dioica L. where "L." refers to Linnaeus. While the name is italicized, the author is not. If a species is moved into a different genus, the original author is put in parentheses and the author who moved it is appended, e.g. Chamaecyparis nootkatensis (D. Don) Spach which was originally described as Cupressus nootkatensis by D. Don. This has been recently moved to a new genus and has now become Xanthocyparis nootkatensis (D. Don) Farjon & Hiep. This addition of authorship is usually only done once in a particular article or citation. In articles where species are described or moved, the date is usually added as well but this is rare in encyclopedic or other non-taxonomic articles.

Hierarchy

The binomial name of a species, of course, only reflects part of the larger classification of the organism:

• Kingdom
• Phylum or Division for plants
• Class
• Order
• Family
• Genus
• Species

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.

Footnote

1. 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.

See also

• Scientific classification
• Evolutionary tree
• Subspecies
• Taxon
• Carolus Linnaeus

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