Cactus

Species of cacti are prominent in many arid and semiarid habitats in the Americas. Cacti provide important elements of the habitat for many species of animals, especially larger species such as saguaro and candelabra cacti.

One of the most familiar groups of cacti are the prickly-pears, beaver-tails, or chollas (Opuntia spp.), of which there are about 300 species. These species have flattened, succulent, segmented stems (sometimes known as stem-joints), and are usually well-armed with spines of various sizes. Opuntia lindheimeri is a red- or yellow-flowered species that grows in Louisiana, Texas, and northeastern Mexico. This plant can reach a height of almost 13 ft (4 m) and can sometimes form dense thickets. Opuntia macrorhiza is a yellow-flowered species that grows in dry prairies from Kansas and Missouri to Texas. Opuntia imbricata has cylindrical instead of flattened stems, grows as tall as 6.6 ft (2 m), has red- or purple-colored flowers, and is commonly known as the tree or candelabra cactus. Opuntia compressa or the beaver-tail is a low-growing, yellow-flowered, eastern species that ranges from Massachusetts to Georgia. Opuntia fulgida or cholla occurs in the Sonora and other deserts of the southwestern United States and Mexico.

The pin-cushion cacti (Mammillaria spp.) are about 300 species of relatively small cacti that have spherical stems, with numerous, small, spiny, nipple-like protuberances on their surface. Mammillaria microcarpa and M. thornberi are species native to the southwestern states and Mexico.

The hedge or candelabra cacti (Cereus spp.) are made up of about 40 species. The barbed-wire cactus (Cereus pentagonus) is an arching, sometimes climbing species that grows in southern Florida, while the organ-pipe cactus (C. thurberi) is an erect, multi-stemmed species of deserts of Arizona and Mexico, which can achieve a height greater than 39 ft (12 m). The desert night-blooming cereus (C. greggii) occurs in deserts of the southwestern United States and Mexico. The odorous, nectar-rich, white flowers of this species open synchronously on only a few nights each year, and are pollinated by bats and hawk moths.

The saguaro, giant, or tall cactus (Carnegiea giganteus, sometimes known as Cereus giganteus) is a spectacular, multi-columnar species that dominates the landscape of deserts of Arizona and down into Mexico. This candelabra-like species can grow as tall as 49 ft (15 m) and has showy flowers that are pollinated by bats, birds, moths, and bees. The saguaro is an important component of the habitat of many species of animals. The gila woodpecker (Centurus uropygalis) and gilded flicker (Colaptes chrysoides) excavate nesting cavities in the saguaro cactus, and when these are abandoned they may be used secondarily by elf owls (Micrathene whitneyi) and other species of birds. The cactus wren (Campylorhynchus brunneicapillus) is another prominent species in saguaro-dominated deserts. In addition, many species of animals feed on the nectar of the saguaro, and on the bright-red, juicy pulp of its ripened fruits.

The barrel cacti (Echinocactus spp.) are seven species with stout, rotund, barrel-like stems. The barrel cactus (Echinocactus polycephalus) is a relatively large species of the southwestern states and Mexico, while the horse crippler (E. texensis) and star cactus (E. asterias) are smaller species. The hedgehog cacti (Echinocereus spp.) are 70 species with relatively small, densely aggregated, spiny stems. The red-flowered hedgehog cactus (E. triglochidiatus) occurs widely in arid habitats of the southwestern United States and Mexico. The organ-pipe cacti (Lemaireocereus spp.) are 25 species of tall, multi-stemmed, columnar cacti, including the candebobe (L. weberi) of Mexico. The barrel cacti (Ferocactus spp.) are 35 species of stout, short-columnar species, including F. acanthodes, F. wislizenii, and F. covillei of the southwestern states and Mexico.