Is "cacti" the correct plural?
Executive summary
The short answer: cacti is a correct plural of cactus, but it is not the only correct form; English allows cactuses (and sometimes unmarked cactus in certain constructions) as acceptable alternatives, with cacti favored in scientific or formal contexts and cactuses common in everyday usage [1] [2] [3].
1. The linguistic origin that made "cacti" common
The form cacti comes from Latin pluralization of words ending in -us, and that Latin legacy explains why many style guides and botanical contexts prefer cacti as the plural of cactus [4] [5]; dictionaries routinely list cacti as a standard plural option and record its pronunciation and use [2].
2. The straightforward English alternative: "cactuses" is legitimate
English also permits regular plural formation, producing cactuses by adding -es, and many modern usage guides and general-audience sites explicitly state that both cacti and cactuses are correct, with cactuses following ordinary English rules and often appearing in everyday speech [1] [6] [5].
3. Style, context and register decide which to use
Writers working in scientific, botanical or more formal registers often prefer the Latin plural cacti because it aligns with taxonomic conventions and established usage in academic texts [1] [7], whereas conversational prose, copyediting for broad audiences, and some dictionaries accept cactuses without stigma [4] [2].
4. Dictionaries and usage panels: consensus and nuance
Major dictionaries and usage resources document both plurals: Merriam‑Webster lists cacti and cactuses (and notes cactus can sometimes remain unchanged), usage sites and grammar books advise cacti for formality while acknowledging cactuses as acceptable, showing consensus that both forms are in current use [2] [4] [3].
5. Conflicting signals: prescriptivists, descriptivists and the OED note
Some prescriptivist commentators insist Latin-derived plurals are “correct” and treat cacti as the only proper option, while descriptivists point out that current common usage includes cactuses and even uninflected cactus in specific contexts; the OED’s editorial choices have historically been cautious on prescribing one plural and record variable use, reflecting that dictionaries often describe rather than dictate usage [8] [9].
6. Real-world practice and style guidance for writers
Practical guidance: mirror the register—use cacti in scientific papers, field guides and formal prose; cactuses is perfectly serviceable in journalism, fiction, and everyday conversation; consult a publication’s style guide if one exists, but no mainstream authority bans either plural [1] [7] [6].
7. Limits of this report and a final judgment
Reporting across grammar manuals, dictionaries and usage sites shows a clear, repeated conclusion: cacti is correct and commonly preferred in formal/scientific contexts, but it is not uniquely correct—cactuses is an equally acceptable English plural in many contexts, and sources document this duality rather than a single prescriptive rule [3] [5] [6]. If a stricter prescription exists within a specific institutional style manual, that would override general practice, but those specifics are beyond the cited sources.