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.
Curt Backeberg was a German horticulturist especially known for the collection and classification of cacti.
Echinopsis is a large genus of cacti native to South America, sometimes known as hedgehog cactus, sea-urchin cactus or Easter lily cactus. One small species, E. chamaecereus, is known as the peanut cactus. The 128 species range from large and treelike types to small globose cacti. The name derives from echinos hedgehog or sea urchin, and opsis appearance, a reference to these plants' dense coverings of spines.
Cleistocactus is a genus of flowering plants in the cactus family Cactaceae, native to mountainous areas - to 3,000 m (9,843 ft) - of South America. The name comes from the Greek kleistos meaning closed because the flowers hardly open.
Pereskia is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French botanist. The genus was more widely circumscribed until molecular phylogenetic studies showed that it was paraphyletic. The majority of species have since been transferred to Leuenbergeria and Rhodocactus. Although Pereskia does not resemble other cacti in its overall morphology, close examination shows spines developing from areoles, and the distinctive floral cup of the cactus family.
In 1984, the International Organization for Succulent Plant Study set up a working party, now called the International Cactaceae Systematics Group, to produce a consensus classification of the cactus family, down to the level of genus. Their classification has been used as the basis for systems published since the mid-1990s. Treatments in the 21st century have generally divided the family into around 125–130 genera and 1,400–1,500 species, which are then arranged in a number of tribes and subfamilies. However, subsequent molecular phylogenetic studies have shown that a very high proportion of the higher taxa are not monophyletic, i.e. they do not contain all of the descendants of a common ancestor. As of March 2017, 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.
Jasminocereus is a genus of cacti with only one species, Jasminocereus thouarsii, endemic to the Galápagos Islands, territorially a part of Ecuador. In English it is often called the candelabra cactus. At maturity it has a branched, treelike habit, and may be up to 7 m (23 ft) tall. The stems are made up of individual sections with constrictions between them. Its creamy white to greenish flowers open at night and are followed by greenish to reddish fruits.
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.
Calymmanthium is a monotypic genus of primitive tree-like cacti from northern Peru. The only species is Calymmanthium substerile. It belongs to the tribe Lymanbensonieae. Calymmanthium is absolutely unique among flowering plants in the mode of its floral development. The young flower is completely encased within the plant's stem until it is fully developed, at which time a crack develops in the stem, allowing pollinators access.
Copiapoa is a genus of flowering plants in the cactus family Cactaceae, from the dry coastal deserts, particularly the Atacama Desert, of northern Chile.
Hatiora is a small genus of epiphytic cacti which belongs to the tribe Rhipsalideae within the subfamily Cactoideae of the Cactaceae. Recent taxonomic studies have led to the three species formerly placed in subgenus Rhipsalidopsis being removed from the genus, including the well known and widely cultivated ornamental plants known as Easter cactus or Whitsun cactus.
The lava cactus is a species of cactus, Brachycereus nesioticus, the sole species of the genus Brachycereus. The plant is a colonizer of lava fields – hence its common name – where it forms spiny clumps up to 60 cm (24 in) tall. Its solitary white or yellowish white flowers open in the daytime. It is endemic to the Galápagos Islands.
Haageocereus is a genus of cacti endemic to the lower elevations of the extremely dry desert along the coast of Peru and northern Chile.
Weingartia is a genus in the family Cactaceae, with species native to Bolivia and Argentina.
Soehrensia spachiana, commonly known as the golden torch, (white) torch cactus or golden column, is a species of cactus native to South America. Previously known as Trichocereus spachianus for many years, it is commonly cultivated as a pot or rockery plant worldwide. It has a columnar habit, with a lime-green cylindrical body with 1–2 cm long golden spines.
Opuntioideae is a subfamily of the cactus family, Cactaceae. It contains 15 genera divided into five tribes. The subfamily encompasses roughly 220–250 species, and is geographically distributed throughout the New World from Canada, to Argentina. Members of this subfamily have diverse habits, including small geophytes, hemispherical cushions, shrubs, trees, and columnar cacti consisting of indeterminate branches or determinate terete or spherical segments.
Armatocereus rauhii is a tall, branched columnar species of cactus endemic to the north of Peru on the western slopes of the Andes.
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.
Neoraimondia arequipensis, synonym Neoraimondia macrostibas, is a tree-like cactus native to western Peru. It was first described in 1835 as Cereus arequipensis.
Neowerdermannia chilensis is a species of Neowerdermannia found in Argentina, Bolivia, Chile, and Peru
