Binomial Nomenclature Rules

Reviewed by: BD Editors

It is important to have rules for naming species using binomial nomenclature (also called binomial, binominal or binary names) so that everyone does it in a uniform way to create brief and unique names that can be used and understood worldwide. The International Code of Zoological Nomenclature and the International Code of Nomenclature for Algae, Fungi and Plants are the two main governing bodies that establish and enforce the rules for binomial nomenclature. There are some specific rules for certain naming situations, but below is a summary of the major ones.

General Rules for Creating Binomial Names

Binomial names consist of two parts, the genus and the species which are always written in modern Latin. Either the genus and/or species name can be derived from words in any language. When referring to the name of a species of organism, the genus and species names are both used. For example, the human species is referred to as Homo sapiens.

The Genus

The genus name is also called the generic name and always begins with a capital letter. For example, binomial name for cats is Felis catus. The genus name must be unique within each kingdom (see image below) but the same genus can be used in more than one kingdom.

The Species

The species within the genus is known by other names depending on the discipline. For general usage, the species is also called the specific descriptor. In botany, it is called the specific epithet and specific name in used in zoology. A species name can be used more than once within a kingdom.

The species name always begins with a lower case letter. It can be a noun or an adjective and it must agree with the Latin gender of the genus name; masculine, feminine or neuter. For example, if the gender of the genus is masculine, the species name should end in -us, -a or -um. An example of this is Passer domesticus, the house sparrow, in which Passer has a masculine gender. Endings for feminine species names include -is and -e and -or is used for neuter genders.

Writing Using Binomial Names

Binomial names are always written in italics. In general practice, the font used for the italics should be different from the font used for the rest of the text. For binomial names written by hand, the genus and species are to be underlined separately. For example, Tyrannosaurus rex.

Using Abbreviations of Binomial Names

If a binomial name is repeated several times in a report or paper, the genus can be written in full the first time it is used and in an abbreviated form from that point on. The abbreviation is created using the first letter of the genus and a period. For example, after using the full binomial name of the blue whale, Balaenoptera musculus in the text, it can be written as B. musculus from that point on. This rule is also used if several species of the same genus are listed or discussed.

The abbreviations “spp.” (plural) or “sp.” (singular),” meaning “several species” and “species,” respectively, are used when the binomial name of a species does not need to be specified or cannot be specified. Italics are not used for the abbreviations. An example of this usage is writing “Acer spp.” to refer to any species of maple tree within the genus Acer. If a writer uses the singular form such as “Acer sp.,” this refers to an unspecified species in the genus Acer, or perhaps a newly discovered species of maple tree.

Taxonomic classification
The image above shows how the binomial nomenclature for on organism emerges out of the overall organization of taxonomic classification. Note that the species name of an organism is designated using the binomial name. The levels of organization above species are called taxa.


  • Binomial nomenclature. (n.d.). In Wikipedia. Retrieved June 17, 2017 from
  • Binomial nomenclature. (2017, June 17). In New World Encyclopedia online. Retrieved from

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MLAAPAChicago Editors. "Binomial Nomenclature Rules." Biology Dictionary,, 25 Jun. 2017, Editors. (2017, June 25). Binomial Nomenclature Rules. Retrieved from Editors. "Binomial Nomenclature Rules." Biology Dictionary., June 25, 2017.

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