Binomial Nomenclature

Binomial nomenclature involves organizing an organism's scientific name into a combination of two terms. These terms are the genus name and the species. Both of these terms are italicized and the genus name is also capitalized.

Linnaeus's taxonomy system has two main features that contribute to its ease of use in naming and grouping organisms. The first is the use of binomial nomenclature and the second is the ordering of species into broad categories.

In biology, binomial nomenclature is the formal system of naming species. The system is called binominal nomenclature (particularly in zoological circles), binary nomenclature (particularly in botanical circles), or the binomial classification system. The essence of it is that each species name is in (modern scientific) Latin and has two parts, so that it is popularly known as the "Latin name" of the species, although this terminology is frowned upon by biologists and philologists, who prefer the phrase scientific name. Instead of using the seven-category system in naming an organism, Carl Linnaeus chose to use a two-word naming system. He adopted the binomial nomenclature scheme, using only the genus name and the specific name or epithet which together form the species name. For example, humans belong to genus Homo and their specific name is sapiens. Humans are then as a species classified by Linnaeus as Homo sapiens. Note that the first name, the genus, is capitalized, while the second is not.

Species is the lowest rank in this system for classifying organisms.

The present system of binomial nomenclature identifies each species by a scientific name of two words, Latin in form and usually derived from Greek or Latin roots. The first name (capitalized) is the genus of the organism, the second (not capitalized) is its species. The scientific name of the white oak is Quercus alba, while red oak is Quercus rubra. The first name applies to all species of the genus— Quercus is the name of all oaks—but the entire binomial applies only to a single species. Many scientific names describe some characteristic of the organism ( alba = white; rubra = red); many are derived from the name of the discoverer or the geographic location of the organism. Genus and species names are always italicized when printed; the names of other taxa (families, etc.) are not. When a species (or several species of the same genus) is mentioned repeatedly, the genus may be abbreviated after its first mention, as in Q. alba. Subspecies are indicated by a trinomial; for example, the southern bald eagle is Haliaeetus leucocephalus leucocephalus, as distinguished from the northern bald eagle, H. leucocephalus washingtoniensis.

The advantages of scientific over common names are that they are accepted by speakers of all languages, that each name applies only to one species, and that each species has only one name. This avoids the confusion that often arises from the use of a common name to designate different things in different places, or from the existence of several common names for a single species. There are two international organizations for the determination of the rules of nomenclature and the recording of specific names, one for zoology and one for botany. According to the rules they have established, the first name to be published (from the work of Linnaeus on) is the correct name of any organism unless it is reclassified in such a way as to affect that name (for example, if it is moved from one genus to another). In such a case definite rules of priority also apply.

Using binomial nomenclature in writing: conventions & grammar

Binomial nomenclature, commonly called Latin or scientific names, is the way each living species is given a unique and universal identity. It is composed of two parts; the genus and the specific epithet. Combined this constitutes the species name. For example, red alder, Alnus rubra; Alnus is the genus and rubra is the specific epithet. There are many species in the genus Alnus but only one Alnus rubra. A species may be further described according to subspecies or variety. For example Ponderosa pine, Pinus ponderosa var. ponderosa or lodgepole pine, Pinus contorta subsp. latifolia. A subspecies is a morphologically distinct, often geographically separate population of a species. A variety is also a morphologically different population which may be associated with a geographic region or particular site conditions but less distinct than a subspecies.

Common names are problematic since many species have more than one common name and a common name can describe more than one species. When writing a scientific document it is the convention to use binomial nomenclature. The species name should always be used in conjunction with common names so that anyone reading the document can know exactly which species you are referencing. There are three common ways to do this:
1. red alder, Alnus rubra
2. red alder (Alnus rubra)
3. Alnus rubra (red alder, Oregon alder)

Regardless of the style chosen the rules are:
  • Always italicize the species name, variety, and subspecies names
  • Abbreviate variety to var. and subspecies to subsp. These are not italicized.
  • If the species is undetermined but the genus known then use the abbreviation for species, spp. This is not italicized. For example Vicia spp.
  • With common names only adjectives derived from proper nouns such as a person or place name are capitalized . For example, western red cedar, Sitka spruce, Douglas-fir, low Oregon-grape, Puget Sound gumweed, etc. Of course if you begin a sentence with a common name then the first letter of the first word is capitalized regardless. Cardinal directions are not capitalized e.g. western hemlock.
  • Dashes between words are used in two circumstances 1) to link two descriptive adjectives e.g. red-flowering currant, small-fruited bulrush, big-leaf maple and 2) when the descriptor is 'false' e.g. Douglas-fir is not a 'true' fir, tall Oregon-grape is not a true 'grape, etc.
  • In subsequent references to a species after the first reference it is common to abbreviate the genus, for example A. rubra, unless another species is being referenced with the same first letter for the genus and the same specific epithet (there are many very common specific epithets like vulgaris, occidentalis, sativum, arvense, macrophyllum, parviflorus, etc.). In that case the genus would need to be specified.
  • If there is more than one widely used common name then they should be listed once at the first reference for clarity. For example Cornus sericea (red-twig dogwood, red-osier dogwood)

The adoption of a system of binomial nomenclature is due to Swedish botanist and physician Carolus Linnaeus (1707 – 1778) who attempted to describe the entire known natural world and gave every species (mineral, plant, 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.

Value of binomial nomenclature
The value of the binomial nomenclature system derives primarily from its economy, its widespread use, and the stability of names it generally favors:
  • The same name can be used all over the world, in all languages, avoiding difficulties of translation.
  • Although such stability as exists is far from absolute, the procedures associated with establishing binomial nomenclature tend to favor stability. 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.

Derivation of names
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 inside-jokes and puns.
  • However, names are always treated grammatically as if they were a Latin phrase.
  • There is a list of Latin and Greek words commonly used in systematic names.
  • Family names are often derived from a common genus within the family.
  • The genus name must be unique inside each kingdom. It is not normally a noun in its Latin grammar.
  • The specific descriptor is also a Latin word but it can be grammatically any of various forms including these:
    • another noun nominative form in apposition with the genus; the words do not necessarily agree in gender. For example, the lion Panthera leo.
    • a noun genitive form made up from 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 necessarily (if ever) the person who names the species; for example Anthus hodgsoni was named by Charles Wallace Richmond, not by Hodgson.
    • a noun genitive form made up from a place name, as with Latimeria chalumnae ("of Chalumna").
    • the common noun genitive form (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".
    • an ordinary Latin or New Latin adjective, as in the house sparrow Passer domesticus where domesticus (= "domestic") simply means "associated with the house" (or "... with houses").
  • Specific descriptors are commonly reused (as is shown by examples of hodgsonii above).

Codes of nomenclature
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 (ICTV). These Codes differ.
  • For example, 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 Carolus Linnaeus first published Species Plantarum), in zoology in 1758. Bacteriology started anew, with a starting point on 1980-01-01.

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.

Although the fine detail will differ, 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 typeface (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 specific name is never written with an initial capital.
    For example, the entire tiger species is Panthera tigris
  • Some older works, on the other hand, would sometimes write the specific name with an initial capital.
  • There are several terms for this two-part species name; these include binomen (plural binomina), binomial, binomial name, binominal, 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. 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 Black 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 scientist who first published the classification. If the species was assigned in the description to a different genus from that to which it is assigned today, the abbreviation or name of the describer and the description date is set in parentheses.
    For example: Amaranthus retroflexus L. or Passer domesticus (Linnaeus, 1758) — the latter was originally described as member of the genus Fringilla, hence the parentheses.
  • When used with a common name, the scientific name usually follows in parentheses.
    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; 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, in a list of members of the genus Canis, when not first in the list Canis lupus becomes C. lupus. 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 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.", meaning "one species of the genus Canis".
  • Easily confused with the foregoing usage is the abbreviation "ssp." (zoology) or "subsp." (botany) indicating an unspecified subspecies; "sspp." or "subspp." indicates "a number of subspecies".
  • 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.

Some References on Binomial Nomenclature

  • Sneath, P. H. A.. "A short history of the Bacteriological Code".
  • Heather Silyn-Roberts (2000). Writing for Science and Engineering: Papers, Presentation. pp. 198.
  • "Recommendation 60F". International Code of Botanical Nomenclature, Vienna Code. 2006. 60F.1.
  • Charles F. Sturm, Timothy A. Pearce, Ángel Valdés (editors) (2006). The Mollusks: A Guide to Their Study, Collection, and Preservation. pp. 147.
  • Frank A. Bisby, Plant Names in Botanical Databases, Plant Taxonomic Database Standards No. 3, Version 1.00, December 1994, Published for the International Working Group on Taxonomic Databases for Plant Sciences (TDWG) by the Hunt Institute for Botanical Documentation, Carnegie Mellon University, Pittsburgh