The classification of living organisms relies on a standardized, two-part naming system known as binomial nomenclature. This system provides every species with a unique scientific name, using Latin grammatical forms to ensure scientists worldwide refer to the exact same organism, regardless of language or regional common names. A complete scientific name consists of two terms: the generic name, which identifies the organism’s genus, and the specific epithet, which distinguishes the species within that genus.
This standardization prevents the confusion caused by common names, which can vary widely or refer to multiple species in different locations. Codes like the International Code of Zoological Nomenclature and the International Code of Nomenclature for algae, fungi, and plants govern these names. These codes ensure that every organism has only one correct scientific name, maintaining clarity in biological communication.
Core Formatting Rules
The scientific name must be presented in the proper sequence, with the genus always preceding the species epithet. For example, the scientific name for the domestic dog is Canis familiaris.
Formatting requires careful attention to capitalization and typeface. The first letter of the generic name is always capitalized, while the specific epithet is never capitalized, even if derived from a proper noun. When typed, both parts of the name must be italicized to set them apart from the surrounding text.
When the name is handwritten, the convention shifts from italics to underlining to maintain distinction. The name of the person who first described the species, known as the authority, is often included in formal taxonomic literature but is usually omitted in general writing. When included, the authority’s name, such as “Linnaeus,” follows the species epithet and is written in standard, non-italicized font.
Subsequent Use and Abbreviation
After a species has been fully introduced with its complete binomial name, subsequent mentions can use a standard abbreviation. This is achieved by reducing the generic name to its capitalized first letter, followed by a period. For instance, once Tyrannosaurus rex has been written out, it can be referred to as T. rex.
Even in its abbreviated form, the scientific name must maintain italicization, including the genus initial and the species epithet. This abbreviation rule holds only if there is no possibility of confusion with another genus mentioned in the text that shares the same initial letter. If a text discusses both Escherichia coli and Enterobacter, both genera must be spelled out in full to prevent ambiguity.
For situations where the species identity is unknown or when referring to a group of species within a genus, specific non-italicized abbreviations are used. The abbreviation ‘sp.’ (species singular) refers to an unconfirmed single species within a genus, such as Canis sp. To refer to multiple species, the plural abbreviation ‘spp.’ is used, as in Canis spp.
Dealing with Trinomials and Classifications Below Species
While the binomial name covers most organisms, some require a three-part name, known as a trinomial, to designate a classification below the rank of species. This system is typically used to identify a subspecies, which is a distinct, geographically isolated population within a species. The trinomial name includes the genus, the species epithet, and a third, subspecific epithet.
In botanical nomenclature, the third name is preceded by a non-italicized abbreviation of the rank, such as ‘subsp.’ for subspecies or ‘var.’ for variety. For example, a botanical subspecies might be written as Pinus contorta subsp. murrayana. Zoological nomenclature is simpler, typically omitting the rank indicator and presenting all three italicized names consecutively, such as Bison bison bison.
A different convention is used for cultivated plants, which are classified below the species level using the term cultivar. These specific names are added after the species name and are enclosed in single quotation marks, without the use of italics. An example would be Salvia guaranitica ‘Blue Enigma’.