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.
Weberocereus is genus of cacti. It produces a green and white flower and is found mainly in Costa Rica and Nicaragua.
Copiapoa is a genus of flowering plants in the cactus family Cactaceae, from the dry coastal deserts, particularly the Atacama Desert, of northern Chile.
Cephalocereus is a genus of slow-growing, columnar-shaped, blue-green cacti. The genus is native to Mexico.
Polaskia is a genus of tree-like cacti reaching 4–5 m high, comprising 2 species. Both present primitive characteristics, but Polaskia chichipe is nearer to Myrtillocactus while Polaskia chende is nearer to Stenocereus. The genus is found in the Mexican states of Puebla and Oaxaca.
Vatricania is a monotypic genus of flowering plants belonging to the family Cactaceae. It just contains one species, Vatricania guentheri(Kupper) Backeb.Greenm. ex Gleason It has the common name of Red Tail Cactus.
Rhodocactus is a genus of flowering plant in the cactus family Cactaceae, native to central South America. Unlike most species of cacti, Rhodocactus has persistent leaves and a fully tree-like habit. The genus was sunk into a broadly circumscribed Pereskia, but molecular phylogenetic studies from 2005 onwards showed that with this circumscription Pereskia was paraphyletic, and in 2016, Rhodocactus was restored for southern South American species.
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.
Rhodocactus grandifolius is a species of cactus native to eastern and southern Brazil. Like all species in the genus Rhodocactus and unlike most cacti, it has persistent leaves. It was first described in 1819. It is grown as an ornamental plant and has naturalized outside its native range.
Praecereus is genus of cactus. It is sometimes included in the genus Cereus.
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.
Parodia magnifica is a species of flowering plant in the family Cactaceae, native to southern Brazil. One of several species called ball cactus, it grows to 7–15 cm (3–6 in) tall by 45 cm (18 in) broad, with heavily ribbed, spherical to columnar, spiny and hairy stems, bearing pale yellow flowers in summer. Its natural habitat is cool, dry temperate grassland at elevations of up to 800 m (2,600 ft). Populations are sparse and fragmented, and it has been designated as “Endangered” by the IUCN Red List.
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.
Parodia ottonis, also known as Indian head cactus, is a cactus found in Argentina, Brazil, Paraguay and Uruguay. There are two recognized subspecies. The epithet ottonis honors the German botanist Christoph Friedrich Otto.
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.
