A cactus is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word "cactus" derives, through Latin, from the Ancient Greek κάκτος, kaktos, 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. Most cacti live in habitats subject to at least some drought. Many live in extremely dry environments, even being found in the Atacama Desert, one of the driest places on earth. Cacti show many adaptations to conserve water. 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 leaves, enlarged stems carry out photosynthesis. Cacti are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north—except for Rhipsalis baccifera, which also grows in Africa and Sri Lanka.
Gymnocalycium, commonly called chin cactus, is a genus of about 70 South American species of cactus. The genus name Gymnocalycium refers to the flower buds bearing no hair or spines.
Schlumbergera is a small genus of cacti with six to nine species found in the coastal mountains of south-eastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite different in appearance from their desert-dwelling cousins. Most species of Schlumbergera have stems which resemble leaf-like pads joined one to the other and flowers which appear from areoles at the joints and tips of the stems. Two species have cylindrical stems more similar to other cacti. Recent phylogenetic studies using DNA have led to three species of the related genus Hatiora being transferred into Schlumbergera, though this change is not universally accepted.
Cephalocereus senilis, the old man cactus, is a species of cactus native to Guanajuato and Hidalgo in eastern Mexico. It is threatened in the wild, but widespread propagation and popularity in cultivation have reduced the demand on wild populations.
Opuntia ficus-indica, the prickly pear, is a species of cactus that has long been a domesticated crop plant grown in agricultural economies throughout arid and semiarid parts of the world. Likely having originated in Mexico, O. ficus-indica is the most widespread and most commercially important cactus.
The Cactoideae are the largest subfamily of the cactus family, Cactaceae. Around 80% of cactus species belong to this subfamily. 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.
Rhipsalis pilocarpa, the hairy-fruited wickerware cactus, is a species of flowering plant in the cactus family that is endemic to Brazil. Scarce in the wild, it is known only in a small number of isolated locations. Its status is listed as “vulnerable” by the IUCN Red List. However, it is cultivated as an ornamental houseplant and as such has gained the Royal Horticultural Society’s Award of Garden Merit.
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.
Gymnocalycium saglionis is a globular cactus species endemic to Argentina, in southern South America.
Gymnocalycium horstii is a globular cactus resembling a loaf of bread from a bakery. Plants have a squat appearance and spines that are curved back towards the body. Plants usually offset over time, creating interesting specimens. The body of this species is glossy and the flower is always white. Its close relative Gymnocalycium buenekeri which occurs 200 km westward has a very similar but dull body with always pink flowers. Gymnocalycium horstii is a very rare and threatened South American species and occurs only in the southern Brazilian province of Rio Grande do Sul.
Opuntia humifusa, commonly known as the devil's-tongue, Eastern prickly pear or Indian fig, is a cactus of the genus Opuntia present in parts of eastern North America.
The saguaro is a tree-like cactus species in the monotypic genus Carnegiea, that can grow to be over 12 meters tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains and Imperial County areas of California. The saguaro blossom is the state wildflower of Arizona. Its scientific name is given in honor of Andrew Carnegie. In 1994, Saguaro National Park, near Tucson, Arizona, was designated to help protect this species and its habitat.
Gymnocalycium mihanovichii is a species of cactus from South America. The most popular cultivars are varied mutants which completely lack chlorophyll, exposing the red, orange, or yellow pigmentation. These mutant strains are often grafted onto the hylocereus cactus, and the combined plant is called a "Moon Cactus". Moon cacti are commonly grown as houseplants and are also known as Ruby Ball, Red Cap, Red Hibotan, or Hibotan cacti.
Gymnocalycium nova is a globular cactus. Plants have a round appearance and spines that are curved back towards the body. The cactus grows in South America, enjoys full sunlight, and is very drought resistant. The species includes the cultivar 'Sierra Medina'.
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 arnostiana 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.
Escobaria minima is a rare species of cactus known by the common names Nellie cory cactus, Nellie's pincushion cactus, birdfoot cactus, and others. It is a very popular species among cactus collectors. This is one reason why it is a highly endangered species in the wild today. This cactus is found only in Brewster County, Texas, in the United States, where there are three populations remaining near Marathon. The cactus is limited to one outcrop in the Marathon Uplift, where it grows in rocky novaculite soils. It was added to the endangered species list in 1979.
Gymnocalycium quehlianum, the Quehla chin cactus, is a species of flowering plant in the family Cactaceae, native to northern Argentina.
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.
Gymnocalycium uruguayense is a species of Gymnocalycium from Brazil and Uruguay.
