In biology, trinomial nomenclature refers to names for taxa below the rank of species. These names have three parts. The usage is different in zoology and botany.
In zoological nomenclature, a trinomen (PL trinomina), trinominal name, or ternary name refers to the name of a subspecies. Examples are Gorilla gorilla gorilla (Savage, 1847) for the western lowland gorilla (genus Gorilla, species western gorilla), and Bison bison bison (Linnaeus, 1758) for the plains bison (genus Bison, species American bison).
A trinomen is a name with three parts:
If the generic and specific name have already been mentioned in the same paragraph, they are often abbreviated to initial letters. For example, one might write: "The great cormorant Phalacrocorax carbo has a distinct subspecies in Australasia, the black shag P. c. novaehollandiae".
While binomial nomenclature came into being and immediately gained widespread acceptance in the mid-18th century, it was not until the early 20th century that the current unified standard of trinominal nomenclature was agreed upon. This became the standard mainly because of tireless promotion by Elliott Coues – even though trinomina in the modern usage were pioneered in 1828 by Carl Friedrich Bruch and around 1850 was widely used especially by Hermann Schlegel and John Cassin. As late as the 1930s, the use of trinomina was not fully established in all fields of zoology. Thus, when referring especially European works of the preceding era, the nomenclature used is usually not in accord with contemporary standards.
For algae, fungi, plants, and their fossils, there is an indeterminate number of infraspecific ranks allowed below the level of species. The secondary ranks below the species rank are
These ranks are components of a
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