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.

All the species of Leuenbergeria, Pereskia and Rhodocactus are superficially like normal trees or shrubs and have numerous leaves with a midrib and a flattened blade (lamina) on either side.

Typically, the tube also has small scale-like bracts, which gradually change into sepal-like and then petal-like structures, so the sepals and petals cannot be clearly differentiated (and hence are often called "tepals").

[10] A small number of cactus species in the tribes Hylocereeae and Rhipsalideae have become adapted to life as climbers or epiphytes, often in tropical forests, where water conservation is less important.

When sufficiently moist air is present, such as during fog or early morning mist, spines can condense moisture, which then drips onto the ground and is absorbed by the roots.

[11] These may be several times the length of the above-ground body in the case of species such as Copiapoa atacamensis,[11] which grows in one of the driest places in the world, the Atacama Desert in northern Chile.

"Normal" leafy plants use the C3 mechanism: during daylight hours, CO2 is continually drawn out of the air present in spaces inside leaves and converted first into a compound containing three carbon atoms (3-phosphoglycerate) and then into products such as carbohydrates.

[24] More recent studies show that "it is highly unlikely that significant carbon assimilation occurs in the stem"; Pereskia species are described as having "C3 with inducible CAM.

The word "cactus" is derived through Latin from the Ancient Greek κάκτος (kaktos), a name used by Theophrastus for a spiny plant,[26] which may have been the cardoon (Cynara cardunculus).

[27] Later botanists, such as Philip Miller in 1754, divided cacti into several genera, which, in 1789, Antoine Laurent de Jussieu placed in his newly created family Cactaceae.

If Leuenbergeria is a good model of these early cacti, then, although they would have appeared superficially similar to other trees growing nearby, they had already evolved strategies to conserve water (some of which are present in members of other families in the order Caryophyllales).

The "core cacti" show a steady increase in both stem succulence and photosynthesis accompanied by multiple losses of leaves, more-or-less complete in the Cactoideae.

This suggests the family must have evolved after the ancient continent of Gondwana split into South America and Africa, which occurred during the Early Cretaceous, around 143 to 101 million years ago.

Other succulent plants, such as the Aizoaceae in South Africa, the Didiereaceae in Madagascar and the genus Agave in the Americas, appear to have diversified at the same time, which coincided with a global expansion of arid environments.

[44] The alternative theory is the species initially crossed the Atlantic on European ships trading between South America and Africa, after which birds may have spread it more widely.

Other features include a relatively dull color, often white or green; a radially symmetrical shape, often tubular; a smell described as "musty"; and the production of a large amount of sugar-rich nectar.

Early evidence of the use of cacti includes cave paintings in the Serra da Capivara in Brazil, and seeds found in ancient middens (waste dumps) in Mexico and Peru, with dates estimated at 12,000–9,000 years ago.

Their capital from the 15th century was Tenochtitlan (now Mexico City); one explanation for the origin of the name is that it includes the Nahuatl word nōchtli, referring to the fruit of an opuntia.

The fruit of the saguaro (Carnegiea gigantea) has long been important to the indigenous peoples of northwestern Mexico and the southwestern United States, including the Sonoran Desert.

[74] A number of species of cacti have been shown to contain psychoactive agents, chemical compounds that can cause changes in mood, perception and cognition through their effects on the brain.

Attempts by the Roman Catholic church to suppress its use after the Spanish conquest were largely unsuccessful, and by the middle of the 20th century, peyote was more widely used than ever by indigenous peoples as far north as Canada.

Long used by the peoples of Central and North America, demand fell rapidly when European manufacturers began to produce synthetic dyes in the middle of the 19th century.

The conversion of land to agriculture has affected populations of Ariocarpus kotschoubeyanus in Mexico, where dry plains were plowed for maize cultivation, and of Copiapoa and Eulychnia in Chile, where valley slopes were planted with vines.

[93] Grazing, in many areas by introduced animals, such as goats, has caused serious damage to populations of cacti (as well as other plants); two examples cited by Anderson are the Galápagos Islands generally and the effect on Browningia candelaris in Peru.

Latin American examples include Parque Nacional del Pinacate, Sonora, Mexico and Pan de Azúcar National Park, Chile.

Cacti naturally occur in a wide range of habitats and are then grown in many countries with different climates, so precisely replicating the conditions in which a species normally grows is usually not practical.

When cacti are grown in containers, recommendations as to how this should be achieved vary greatly; Miles Anderson says that if asked to describe a perfect growing medium, "ten growers would give 20 different answers".

[99][100][101][102] However, the use of organic material is rejected altogether by others; Hecht says that cacti (other than epiphytes) "want soil that is low in or free of humus", and recommends coarse sand as the basis of a growing medium.

[109][97] Some cacti, particularly those from the high Andes, are fully frost-hardy when kept dry (e.g. Rebutia minuscula survives temperatures down to −9 °C (16 °F) in cultivation[110]) and may flower better when exposed to a period of cold.

These appear to cause only limited visible symptoms, such as chlorotic (pale green) spots and mosaic effects (streaks and patches of paler color).