Plural of “genus”

The plural of genus is genera.

Why

"Genus" is Latin for "birth," "origin," or "kind," and it belongs to the same Latin declension class as "corpus" — third-declension and neuter — so its plural is likewise formed with an -a-based ending rather than -i, giving "genera" rather than anything resembling "cacti" or "foci." English borrowed the word specifically for Linnaean biological taxonomy in the 18th century, where a genus groups related species together, sitting between family and species in the classification hierarchy.

Because "genus" functions as precise technical vocabulary within biology rather than as a word that ever drifted into casual everyday speech, "genera" has remained essentially unchallenged as its plural — there is no meaningful competing regularized form the way there is for "focus" or even "cactus," since the word's entire existence in English has been within a field that carefully preserves its Latin taxonomic terminology.

Usage note

Always use "genera" in any biological, taxonomic, or scientific writing; there's no register in which "genuses" would read as acceptable or expected, unlike some of the more everyday Latin borrowings elsewhere on this list.

Genus names themselves are always capitalized and italicized in scientific writing (as in "Panthera," the genus containing lions and tigers), but the common English plural "genera," referring to genus as a general concept rather than a specific name, is neither capitalized nor italicized. Genus names sometimes honor people or places, a naming convention that has occasionally sparked controversy when a newly described genus is named after someone later found to have behaved badly, and taxonomists debating whether to revise such names still refer to "genera" collectively using the standard Latin plural, since the naming controversy is separate from the grammatical convention itself.

Common real mistakes

"Genuses" occasionally appears in casual nature writing by people unfamiliar with the taxonomic convention, but it's considered nonstandard in any biological or scientific context; the correct form is always "genera."

The wider pattern

"Genus" shares its exact declension pattern with "corpus," both being third-declension neuter Latin nouns pluralizing in -era/-ora rather than -i, which is why the two words offer a useful contrast with "focus" and "cactus," whose different Latin declension produces the more familiar -i plural instead. The rank of genus sits within a strict taxonomic hierarchy (kingdom, phylum, class, order, family, genus, species), and reclassifying a species into a different genus, or splitting one genus into several, remains one of the more contentious ongoing debates in modern biology as genetic sequencing reveals relationships earlier naturalists couldn't have known about.

Examples

• The field guide organizes birds by family, then by genera within each.
• Scientists have described several new genera of beetles in the past decade.
• The two genera share a common ancestor but diverged millions of years ago.
• Botanists reclassified several plant genera after new genetic evidence emerged.
• The textbook lists dozens of genera within the cat family alone.
• Researchers compared genera across three separate island ecosystems.
• Several genera once thought distinct have since been merged into one.
• The museum's collection spans hundreds of genera across multiple phyla.
• New genera continue to be identified as DNA sequencing improves.
• The paper proposes splitting one genus into two entirely separate genera.
• The expedition discovered two previously unknown genera of frogs.
• Taxonomists merged several genera after new fossil evidence emerged.
• The field guide organizes flowering plants into hundreds of genera.
• Scientists debated whether the specimens belonged to existing genera or a new one.
• Genetic testing revealed the species actually belonged to a different genus entirely.
• The revised classification split one large genus into four smaller genera.
• Botanists continue to debate the boundaries between several closely related genera.
• The museum's fossil collection spans dozens of extinct genera.
• The paper proposes reclassifying two genera based on new DNA evidence.
• Several genera in the family remain poorly studied to this day.