Plural of Cactus

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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.

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The Standard Rules for Forming the Plurals

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 donkeys
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.)
Another Interactive Exercise
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See Also

Unusual pluralsPlural forming table Quirks with forming plurals Forming the plurals of abbreviations Forming the plurals of compound nouns