To write a scientific name, capitalize the genus, keep the species epithet lowercase, and italicize both as a single unit — for example, Homo sapiens or Escherichia coli. After first use, abbreviate the genus to its first letter plus a period (E. coli). Subspecies, taxonomic authority citations, and higher ranks like family or order follow separate rules.
The core rule: genus capitalized, species lowercase, both italicized
A binomial (two-part) scientific name has a genus name and a specific epithet. In running manuscript text:
- The genus is capitalized: Homo, Escherichia, Quercus.
- The species epithet is always lowercase, even if it is derived from a proper noun (a person’s name or a place): sapiens, coli, alba.
- Both parts are italicized as a unit: Homo sapiens, Escherichia coli, Quercus alba.
This applies regardless of discipline — the same convention holds in medicine, microbiology, ecology, botany, and zoology manuscripts. It traces back to Linnaean binomial nomenclature and is now codified by the taxonomic governing bodies for each kingdom (see below), and in practice enforced through journal style guides such as the AMA Manual of Style (used widely in biomedical journals) and the Council of Science Editors (CSE) Scientific Style and Format manual.
Abbreviating the genus after first use
Spell the genus name out in full the first time a species is mentioned in the text, the abstract, and typically also the title (check the specific journal’s instructions for authors on the title case). After that first full use, the genus may be abbreviated to its initial letter followed by a period, with the species epithet still lowercase and both still italicized:
- First mention: Escherichia coli
- Subsequent mentions: E. coli
Two situations where you should not abbreviate:
- At the start of a sentence. Most style guides discourage opening a sentence with an abbreviated genus; either spell it out again or restructure the sentence.
- When more than one genus in the paper starts with the same letter. If a manuscript discusses both Streptococcus and Staphylococcus, abbreviating both to S. creates ambiguity — spell out whichever is needed for clarity, or use a distinguishing abbreviation convention the journal permits.
What does and doesn’t get italicized
Only genus, species, and infraspecific epithets (subspecies, variety, forma) are italicized. Taxonomic ranks above genus — family, order, class, phylum — are set in regular (roman) type and capitalized as proper nouns, but not italicized:
- Italicized: Homo sapiens, Canis lupus familiaris
- Not italicized: Hominidae (family), Primates (order), Mammalia (class)
A related, frequently mishandled point: the abbreviations sp. (single unspecified species), spp. (multiple unspecified species), cf. (compare to, used when identification is uncertain), and sp. nov. / gen. nov. (newly described species/genus) are themselves set in regular roman type, not italics — even though they sit directly next to an italicized genus name. For example: Quercus sp. (an unidentified oak species) or Bacillus sp. nov. (a newly described Bacillus species). Common names derived from a scientific name — “E. coli infection” used loosely in prose, or vernacular names like “human” or “white oak” — are not italicized or capitalized as though they were the formal binomial.
Subspecies and trinomial names
When a subspecies is specified, the name becomes a trinomial: genus, species, and subspecies epithet, all three italicized and all lowercase except the genus. For example, Canis lupus familiaris (the domestic dog, a subspecies of Canis lupus). In botany, an infraspecific rank abbreviation such as subsp. or var. is inserted between the species and infraspecific epithet and, like sp., is set in roman type rather than italics: Zea mays subsp. mexicana.
Taxonomic authority (author citation)
In taxonomic and systematics literature, a scientific name is often followed by the name of the person (or people) who first formally described the species and the year of publication, e.g. Homo sapiens Linnaeus, 1758. This author citation is set in regular roman type, not italics, and is not part of the italicized binomial itself. Most manuscripts outside taxonomy/systematics proper — clinical, ecological, or applied research papers that simply use an already-established species name — omit the author citation entirely; include it only if the species’ identity could otherwise be ambiguous or if the journal’s instructions for authors specifically request it.
Which code actually governs the name
For researchers describing a new taxon, formatting is governed by the applicable nomenclatural code, not by house style alone:
- The International Code of Zoological Nomenclature (ICZN) governs animal names.
- The International Code of Nomenclature for algae, fungi, and plants (ICN) governs those groups.
- The International Code of Nomenclature of Prokaryotes (ICNP) governs bacteria and archaea.
For the overwhelming majority of manuscripts — papers that use existing, already-published species names rather than formally describing a new one — a researcher does not need to consult these codes directly; following the journal’s house style (AMA, CSE, or the journal’s own instructions for authors) for capitalization, italics, and abbreviation is sufficient. The codes become directly relevant only when a manuscript formally proposes a new species or genus name, at which point the applicable code’s specific requirements for the description, type specimen, and name formation take priority.
Practical formatting in submission
- In Word: select the genus and species and apply italics (Ctrl+I) directly, rather than relying on autoformat or find-and-replace, which can silently miss instances.
- In LaTeX: use
textit{}oremph{}around the binomial, not manual font-switching commands. - Check plain-text fields separately. Submission systems (Editorial Manager, ScholarOne, and similar platforms) sometimes strip formatting from fields like the plain-text abstract or cover letter body, even when the manuscript file itself is correctly formatted — verify italics survived in every field the journal requires, not just the main manuscript document. The same italics can also be lost in figure legends and axis labels; see CASRAI’s guide to scientific figure rules for journal submission.
- Check the journal’s specific instructions for authors. Most biomedical and life-science journals default to AMA or CSE conventions, but some (particularly in botany and zoology) specify additional requirements, such as always including the author citation on first mention. For the surrounding manuscript formatting rules (margins, fonts, spacing) most journals also specify, see CASRAI’s research paper format guide.
Common mistakes to check for before submission
- Species epithet capitalized (Escherichia Coli — incorrect; should be Escherichia coli).
- Name not italicized at all, or italicized inconsistently across the manuscript.
- Genus abbreviated before it has been spelled out in full at first mention.
- sp., spp., or cf. italicized along with the genus name (they should not be).
- Family/order/class names (e.g., “Hominidae”) italicized as though they were genus-species names (they should not be).
- Author citation (e.g., “Linnaeus, 1758”) set in italics rather than roman type.
Frequently asked questions
How do you write a scientific name in a manuscript?
Capitalize the genus, keep the species epithet lowercase, and italicize both as a unit — for example, Homo sapiens. Spell the genus out in full on first mention, then abbreviate to its initial letter (H. sapiens) afterward, unless doing so would create ambiguity with another genus discussed in the same paper.
Are scientific names italicized in APA and AMA style?
Yes. Both APA and AMA conventions italicize genus and species names. AMA’s rules (the more detailed of the two on this specific point, and the dominant style in biomedical journals) are covered above; for the broader mechanics of an APA-formatted manuscript, see CASRAI’s guide to writing a research paper in APA style.
Is the species name ever capitalized?
No. The species epithet is always lowercase in a properly formatted binomial name, even when it derives from a person’s name (e.g., victoriae) or a place name — only the genus is capitalized.
Do you italicize family, order, or class names?
No. Only genus, species, and infraspecific (subspecies/variety) epithets are italicized. Names for family, order, class, and higher taxonomic ranks are capitalized but set in regular roman type.
What is a trinomial scientific name?
A trinomial adds a subspecies epithet to the standard binomial — genus, species, and subspecies, all three italicized, with only the genus capitalized. Canis lupus familiaris is a common example.
