The family of dicotyledonous plants which includes such genera as Mammillaria (the nipple cacti), Opuntia (chollas), Ferocactus (barrel cacti), Escobaria (beehive cacti), and Carnegiea (saguaros). There are over 90 genera with around 2000 species amongst them.
They are generally fleshy/succulent because they store water in their modified stems. This is an adaptation for surviving in xeric environments as well as having reflective/defensive hairs and spines, and a growth habit which exposes as little surface area as possible to the midday sun.
Cactaceae, the cactus family, contains about 2000 species of plants in 100-200 genera.   Cactaceae are generally succulent plants, adapted for dry conditions.   All have spines, enlarged leaf hairs adapted to protect the leaves from dessicaton, or from being eaten.   Cactaceae are native to North America (NA) and South America (SA), although genus Rhipsalis may be native to South Africa, Madagascar, and various Indian Ocean Islands.

Many cacti are valued as house or garden plants because of their novel forms or beautiful flowers. Some produce edible fruit. Because of their popularity, they have been introduced all over the world, some (especially Opuntia) with devastating effects on local ecologies.

Superkingdom Eukaryota
Kingdom Plantae
Division Magnoliophyta (formerly Phylum Angiospermae)
Class Magnoliopsida (formerly Class Dicotyledonae)
Subclass Caryophyllidae
Order Caryophyllales
Family Cactaceae

Previously, Cactaceae had been divided into three tribes, Pereskieae, Opunitieae,  and Cacteae, with the latter being divided into various subtribes, but biologists have elevated these tribes to the status of subfamilies, with the attendant name changes.

Cactoideae contains most of the family's genera and species, and has been further subdivided into eight tribes (which do not map to the old subtribes of Cacteae).   These associations are still being determined, and some of the tribal assignments listed below are controversial.

Subfamily Pereskoideae:

Subfamily Opuntaceae: Subfamily Cactoideae:

L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000
Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991)

"A Brief Synopsis of Evolution in the Cactus Family" by Dr Robert S. Wallace at

Justin Spiegel's Desert Cactus Page

The Cactus and Succulent Plant Mall:

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