A cactus is a succulent desert plant that's often covered in sharp spines. Some cacti grow brilliantly colored flowers, but none of them have leaves.

You can grow an indoor cactus in a pot — it's a fairly easy plant to care for, since it prefers to be watered infrequently. Cacti are able to conserve water, which is why they do well in very dry environments, like the American Southwest. The Greek root of cactus is kaktos, the name of a specific spiky Sicilian plant.

Definitions of cactus

n any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines

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Acanthocereus pentagonus, Acanthocereus tetragonus, pitahaya, pitahaya cactus
cactus of the southwestern United States and northern Mexico having edible juicy fruit
Aporocactus flagelliformis, rat's-tail cactus, rattail cactus
commonly cultivated tropical American cactus having slender creeping stems and very large showy crimson flowers that bloom for several days
Ariocarpus fissuratus, living rock
usually unbranched usually spineless cactus covered with warty tubercles and having magenta flowers and white or green fruit; resembles the related mescal; northeastern Mexico and southwestern United States
Carnegiea gigantea, saguaro, sahuaro
extremely large treelike cactus of desert regions of southwestern United States having a thick columnar sparsely branched trunk bearing white flowers and edible red pulpy fruit
night-blooming cereus
any of several cacti of the genus Cereus
a cactus of the genus Coryphantha
barrel cactus, echinocactus
any cactus of the genus Echinocactus; strongly ribbed and very spiny; southwestern United States to Brazil
hedgehog cereus
cactus of the genus Echinocereus
rainbow cactus
a stout cylindrical cactus of the southwest United States and adjacent Mexico
epiphyllum, orchid cactus
any cactus of the genus Epiphyllum having flattened jointed irregularly branching stems and showy tubular flowers
barrel cactus
a cactus of the genus Ferocactus: unbranched barrel-shaped cactus having deep ribs with numerous spines and usually large funnel-shaped flowers followed by dry fruits
Easter cactus, Hatiora gaertneri, Schlumbergera gaertneri
spring-blooming South American cactus with oblong joints and coral-red flowers; sometimes placed in genus Schlumbergera
night-blooming cereus
any of several cacti of the genus Hylocereus
Lemaireocereus chichipe, chichipe
tall treelike Mexican cactus with edible red fruit
Lophophora williamsii, mescal, mezcal, peyote
a small spineless globe-shaped cactus; source of mescal buttons
any cactus of the genus Mammillaria
Mammillaria plumosa, feather ball
a low tuberculate cactus with white feathery spines; northeastern Mexico
Myrtillocactus geometrizans, garambulla, garambulla cactus
arborescent cactus of western Mexico bearing a small oblong edible berrylike fruit
Knowlton's cactus, Pediocactus knowltonii
small clustering cactus of southwestern United States; a threatened species
any of several cacti of the genus Nopalea resembling prickly pears
prickly pear, prickly pear cactus
cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock
Opuntia cholla, cholla
arborescent cacti having very spiny cylindrical stem segments; southwestern United States and Mexico
mistletoe cactus
a plant of the genus Rhipsalis
Christmas cactus, Schlumbergera baridgesii, Schlumbergera buckleyi
epiphytic cactus of Brazilian ancestry widely cultivated as a houseplant having jointed flat segments and usually rose-purple flowers that bloom in winter
night-blooming cereus
any of several night-blooming cacti of the genus Selenicereus
Schlumbergera truncatus, Thanksgiving cactus, Zygocactus truncatus, crab cactus
South American jointed cactus with usually red flowers; often cultivated as a houseplant; sometimes classified as genus Schlumbergera
hedgehog cactus
cactus of the genus Echinocactus having stout sharp spines
Echinocactus grusonii, golden barrel cactus
large cactus of east central Mexico having golden to pale yellow flowers and spines
Opuntia lindheimeri, nopal
cactus having yellow flowers and purple fruits
Opuntia tuna, tuna
tropical American prickly pear of Jamaica
Selenicereus grandiflorus, queen of the night
tropical American climbing cactus having triangular branches; often cultivated for its large showy night-blooming flowers followed by yellow red-streaked fruits
Type of:
a plant adapted to arid conditions and characterized by fleshy water-storing tissues that act as water reservoirs

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