Plural of Cactus

The Quick Answer

The plural of cactus is cacti or cactuses.

The Plural of Cactus

The plural of cactus is cacti or cactuses.

Most cacti live in habitats subject to at least some drought.
The great majority of cactuses have no visible leaves.

The noun cactus has a Latin root, which is the derivation of the plural cacti. Through common usage, cactuses (which adheres to the standard rules for forming plurals) is also acceptable.

The table below shows the standard rules for forming the plurals of nouns in English.

Type	Example of Type	Forming the Plural	Plural
Most Nouns	lamp scythe	add s	lamps scythes
Noun Ending s, sh, ch, x or z	cactus dress	add es	cactuses dresses
Nouns ending [consonant] o	hero zero tomato	add either s or es (There are no rules for this - you have to know.)	heroes zeros tomatoes
Nouns ending [vowel] o	patio ratio	add s	patios ratios
Nouns ending [consonant] y	story penny	change the y to an i and add es	stories pennies
Nouns ending [vowel] y	donkey chimney	add s	donkey chimneys
Nouns ending f or fe	dwarf hoof	ves and/or s (There are no rules - you have to know.)	dwarfs hooves or hoofs
Exceptions	man louse	some nouns undergo a vowel or letters change	men lice
More exceptions	salmon sheep	some nouns do not change at all	salmon sheep
Foreign rulings	cactus medium	some nouns adopt foreign rulings	cacti media

Why Is There Confusion over the Plural of Cactus?

Confusion arises over the plural of cactus because its original plural form (cacti) derives from Latin and native English speakers are drawn to cactuses, which adheres to the standard ruling for forming plurals.

Both cactuses and cacti are acceptable. Of note, cacti is the more common plural. (See the evidence in Google's Ngram Viewer.)