A cactus is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1,750 known species of the order Caryophyllales. The word cactus derives, through Latin, from the Ancient Greek word κάκτος (káktos), a name originally used by Theophrastus for a spiny plant whose identity is now not certain. Cacti occur in a wide range of shapes and sizes. They are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north, with the exception of Rhipsalis baccifera, which is also found in Africa and Sri Lanka. Cacti are adapted to live in very dry environments, including the Atacama Desert, one of the driest places on Earth. Because of this, cacti show many adaptations to conserve water. For example, almost all cacti are succulents, meaning they have thickened, fleshy parts adapted to store water. Unlike many other succulents, the stem is the only part of most cacti where this vital process takes place. Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. As well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of true leaves, cacti's enlarged stems carry out photosynthesis.
In botany, areoles are small light- to dark-colored bumps on cacti out of which grow clusters of spines. Areoles are important diagnostic features of cacti, and identify them as a family distinct from other succulent plants. The spines are not easily detachable, but on certain cacti, members of the subfamily Opuntioideae, smaller, detachable bristles, glochids, also grow out of the areoles and afford additional protection.
Echinocereus is a genus of ribbed, usually small to medium-sized, cylindrical shaped cacti, comprising about 70 species native to the southern United States and Mexico in very sunny, rocky places. Usually the flowers are large and the fruit edible.
Armatocereus is a genus of mostly tree-like cacti from South America. These species have a conspicuous constriction at the end of the annual growth. The flowers are mostly white, with a more or less spiny ovary. The fruits are mostly spiny.
Neoraimondia is a genus of medium to large cacti from Peru. The genus is named after the Italian-born Peruvian explorer, naturalist, and scientist, Antonio Raimondi.
Copiapoa is a genus of flowering plants in the cactus family Cactaceae, from the dry coastal deserts, particularly the Atacama Desert, of northern Chile.
Vatricania is a monotypic genus of flowering plants belonging to the family Cactaceae. It contains just one species, Vatricania guentheri. It has the common name of red tail cactus.
Haageocereus is a genus of cacti endemic to the lower elevations of the extremely dry desert along the coast of Peru and northern Chile.
Cacteae is a tribe of plants of the family Cactaceae found mainly in North America especially Mexico. As of August 2018, the internal classification of the family Cactaceae remained uncertain and subject to change. A classification incorporating many of the insights from the molecular studies was produced by Nyffeler and Eggli in 2010. The main threats to cactus species are poaching, farming, mining developments, and climate change.
Selenicereus megalanthus, synonym Hylocereus megalanthus, is a cactus species in the genus Selenicereus that is native to northern South America, where it is known, along with its fruit, by the name of pitahaya. The species is grown commercially for its yellow fruit, but is also an impressive ornamental climbing vine with perhaps the largest flowers of all cacti.
Praecereus is genus of cactus. It is sometimes included in the genus Cereus.
Rhodocactus stenanthus is a species of cactus that is endemic to Brazil. First described as Pereskia stenantha, it was transferred to Rhodocactus in 2016. Like all species in the genus Rhodocactus, and unlike most cacti, it has persistent leaves. In its native locality, it is sometimes used in hedges.
Parodia buiningii is a rare species of cactus native to South America. It is a solitary spherical or oblate cactus only a few inches in height with long, yellow spines. It bears yellow flowers, and produces hairy fruit and black seeds. It is found surrounding the towns of Santana do Livramento, Brazil and Rivera, Uruguay.
Parodia leninghausii is a species of South American cactus commonly found as a houseplant. Common names include lemon ball cactus, golden ball cactus and yellow tower cactus.
Lophocereus marginatus is a species of plant in the family Cactaceae. It is sometimes called Mexican fencepost cactus.
Parodia tenuicylindrica is a species of cactus from the genus Parodia. The small green cacti have yellow and red-brown spines, white wool and yellow flowers. They produce yellow-green fruit, and black seeds. P. tenuicylindrica can be found growing individually in Rio Grande do Sul, Brazil.
Parodia curvispina is a species of cactus in the genus Parodia. The small, squat green plants produce yellow flowers, green fruit and black seeds. The species is found growing in Rio Grande do Sul, Brazil.
Gymnocalycium baldianum, the spider-cactus or dwarf chin cactus, is a species of flowering plant in the cactus family Cactaceae, native to the Catamarca Province in Argentina.
Ferocactus histrix, also known as Acitrón barrel cactus is a species of Ferocactus native to central Mexico. It is a large barrel cactus that can be commonly found throughout all the Central Mexican matorral. It produces an edible fruit appreciated for its sour taste.
Rhodocactus sacharosa, synonym Pereskia sacharosa, is a species of flowering plant in the cactus family Cactaceae, native from Bolivia and west-central Brazil to Paraguay and northern Argentina. Like all species in the genus Rhodocactus and unlike most cacti, it has persistent leaves. It was first described in 1879.
