Binomial nomenclature

Binomial nomenclature identifies a species with a genus name and a specific epithet, written together as a single scientific name.¹ The genus begins with a capital letter, while the specific epithet is lowercase; both are conventionally italicized in print, as in Homo sapiens. The epithet by itself is not the complete species name, because the same epithet can occur in many genera.

Names are generally Latin or Latinized, allowing scientists to communicate across languages and regions. A genus may contain several related species, while the shared first element can signal a taxonomic relationship without serving as a complete statement of ancestry. An author’s name and publication year may follow the binomen in formal contexts, but they are attribution, not part of the two-word name.

The modern system was consolidated by Carl Linnaeus, whose Species Plantarum of 1753 established the starting point for most botanical nomenclature.² Linnaeus had already used two-word labels in earlier works, but the concise binomial format made species names practical for catalogs and scientific prose. Zoological practice developed along a related path and later received its own international rules.

Modern names are regulated by separate codes rather than by one universal rulebook. The International Code of Nomenclature for algae, fungi, and plants governs botanical, fungal, and algal names, while the International Code of Zoological Nomenclature governs animal names.³ These codes establish principles such as priority, valid publication, typification, and the treatment of competing names.

A scientific name becomes nomenclaturally available only when it satisfies the publication and form requirements of the relevant code; merely mentioning a name does not necessarily establish it. The principle of priority usually favors the oldest properly published name, although codes provide exceptions that preserve stability when strict priority would cause widespread disruption.

A species can therefore change names without changing organisms. Revision may move it to another genus, reveal that two names refer to the same species, or show that a historical name has precedence. The original combination can be recorded in parentheses around the author citation when a species is transferred to a different genus. Taxonomic databases, including the NCBI Taxonomy, track such synonyms and changing classifications, but a database entry does not itself replace formal nomenclatural publication.⁴

Binomial nomenclature has several edge cases that ordinary usage conceals. In zoology, a species name is a binomen, whereas a subspecies name is a trinomen that adds a third element; in botany, infraspecific ranks use additional connecting terms and formatting rules.³ Hybrid names may be marked with a multiplication sign, and cultivated plants follow a separate nomenclatural framework from wild species.

Scientific names can also preserve people, places, physical traits, or indigenous words, despite their Latinized grammar. A name’s ending may change to agree with Latin gender when a species moves between genera, and diacritics are normally modified or omitted in Latinization. Most importantly, nomenclature and taxonomy are different: nomenclature governs names, while taxonomy evaluates relationships, boundaries, and classification. A stable name may therefore coexist with substantial debate about what biological entities belong within the species.

Binomen

The two-part scientific name of a species, consisting of a genus and a specific epithet.

Specific epithet

The second element of a species name; it is not, by itself, the complete name.

Priority

The rule that generally gives precedence to the earliest properly published available name.

Type

A specimen, culture, or other nomenclatural reference that anchors the application of a name.

Synonym

A different scientific name that refers to the same taxon under a particular classification.