How Should Genus and Species Names Be Formatted?

Scientific names let biologists refer to organisms precisely across languages and regions. The usual format for a species is a two-part name called a binomial: the genus name followed by the specific epithet. The two words have consistent capitalization and typography rules.

The standard format

Write the genus with an initial capital letter and the specific epithet in lowercase. Italicize both words when typing or typesetting:

• Homo sapiens — humans
• Escherichia coli — a bacterium
• Panthera leo — lions

The genus is the first word; the specific epithet is the second. Strictly speaking, the epithet alone is not the full species name. For example, sapiens by itself does not identify Homo sapiens. When biologists use “species name” informally, they often mean the complete binomial.

These names are Latin or treated as Latin under naming conventions. Many are formed from Greek, other languages, or people’s names and adapted into Latin form. Their spelling is standardized; you generally do not translate or change a scientific name when writing in another language.

A worked example

Suppose you are writing about Escherichia coli. Apply the rules in this order:

1. Put the genus first: Escherichia.
2. Follow it with the specific epithet: coli.
3. Capitalize the genus and lowercase the epithet.
4. Italicize both words: Escherichia coli.

The genus can also appear by itself when you mean the genus as a taxonomic group: “Escherichia contains several species.” The name of a genus is italicized too. By contrast, higher taxonomic ranks are generally not italicized: “the family Enterobacteriaceae” uses roman type for the family name.

Abbreviating the genus

After you have written the full name once, you can often shorten the genus to its first initial and a period. For example, a later mention of Escherichia coli may be written E. coli. Keep the initial capitalized and italicize the abbreviated genus and the epithet.

Abbreviate only when readers can tell which genus you mean. If a passage discusses several genera beginning with the same letter, spell out the genus to avoid confusion. In a formal document, give the full name at its first mention even if you plan to use an abbreviation afterward.

Subspecies and unidentified species

A subspecies name has three parts: genus, specific epithet, and subspecific epithet. Capitalize the genus, lowercase the other two words, and italicize all three. For example, Panthera tigris altaica is a three-part name used for the Amur tiger.

If the species is not known or specified, write the genus followed by sp. for one unspecified species, or spp. for multiple species: Quercus sp. or Quercus spp. Italicize the genus, but leave “sp.” and “spp.” in ordinary type. These abbreviations are not part of a species name, so do not italicize them or add a second period after spp.

Handwriting and plain text

If you are handwriting a scientific name, underline the genus and specific epithet separately: Homo sapiens. This convention indicates that the words should be italicized in print. Do not underline the space between them.

If a plain-text system cannot display italics, use its standard formatting controls where possible. In an informal plain-text message, you can leave the name unstyled if necessary, but preserve its spelling and capitalization. Markdown systems commonly show italics by putting a single asterisk on each side of the name: *Homo sapiens*.

Common mistakes

• Capitalizing both words: Write Canis lupus, not Canis Lupus.
• Italicizing only the genus: Italicize the epithet as well: Canis lupus.
• Using the epithet alone as the formal name: Use the full binomial, such as Canis lupus.
• Italicizing “sp.” or “spp.”: In Quercus sp., only the genus is italicized.
• Abbreviating too soon or ambiguously: Give the full name first, and spell it out again if the abbreviation could refer to more than one genus.

The capitalization and italics make the parts of a scientific name easy to recognize. For a standard species name, remember the pattern: capitalized genus, lowercase epithet, both italicized.