Cactus distribution

Cactus are original from America, although few species from Rhipsalis genus have been found in Africa and India, nevertheless it is assumed that their seeds were introduced by birds or man.
We can find wild cactus in the American continent, from 53º North latitude (States of Alberta and British Columbia, in Canada) to 50º South latitude (Tierra del Fuego, Argentina).
Thus, within the USA inhabit several cactus species in all its states but three (Maine, New Hampshire and Vermont).
But south, Mexico is the country that has the greater variety of genus and species. Within the state of Oaxaca, enormous Pachycereus weberi stand out, with dozens of perfectly vertical stems that grow beyond 2 m. high. There are numerous Cephalocereus senilis, of several meters of height in perfect vertical column, in the state of Hidalgo. On Zopilote Canyon, in the State of Guerrero, there are Neobuxbaumia zopilotensis, Mammillaria guerreronis and the rare Neoewansia zopilotensis among other species. In the great desert plains from the North of Mexico (San Luis Potosi, Nuevo Leon, Tamaulipas, Coahuila and Chihuahua) we can found the greater number of globular cactus of small volume like the mythical Lophophora williamsii, several species of Astrophytum and Mammillaria, as well as Thelocactus bicolor and Mammillopsis senilis.
But cactus do not only live in arid zones. Also they do it in the humid tropical forests, where many epiphytic species which big flowers are opened during the night, can be found.
Following to the South, rain increase, while temperature keeps high, so dense woods can be found and the number of cactus species reduce remarkably.
They appear some epiphytic cactus, that live on trees and rocks. These kind of plants rarely shows spines and their stems usually have the appearance of leaves.
Islands of the Caribbean also have their cactus. Species from Opuntia, Hylocereus and Melocactus genus among others can be found, being Melocactus the more characteristic ones.
Number cactus species increase again when arriving to South America, but without reaching the abundance found in Mexico.
Main populations are in the south of Brazil, in Argentina, Bolivia, Chile, Peru, Paraguay and Uruguay.
In the Eastern but dry zones of Brazil we can find a great quantity of columnar cactus (Cereus, Cephalocereus, Monvillea, etc.). These plants grow generally between the dense vegetation.
To the South and the East of Brazil there are some epiphytic species like Zygocactus, Schlumbergera and Rhipsalis. But towards the interior there are Discocactus, Melocactus, Gymnocalycium, Notocactus, etc.
In the western slope of the Andes the conditions are very special. In a large area of Peru and Bolivia the climate is very dry and the life of the wild plants gets to depend almost entirely on fog. In Andean slopes Espostoa and Oreocereus vegetate and there are cactus until the 4,000 meters of altitude in places almost permanently covered by snow.
We can find Opuntia, Matucana, Oroya and Lobivia all over the Altiplano.
In Chile, columnar cactus like Browningia and Eulychnia and other subglobular cactus like Copiapoa and Neoporteria, are present.
Crossing the Andes, in the Argentine regions with dry grass, we can find small globular cactus like Rebutia, Gymnocalycium, Parodia, Notocactus and Echinopsis, and columnar like Trichocereus.
Cleistocactus can be found from the center of Peru, passing through the East of Bolivia, besides from Paraguay, Argentina and Uruguay.