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Family: Cactaceae

Kingdom: Plantae Rank: Family Parent: Caryophyllales Status: Valid

Common Names:

  • CACTUS FAMILY - English, United States of America

Morphological Description

Family Recognition in the Field: Leafless stem succulents with watery sap, areoles (= pad-like axillary buds unique to the family) typically bearing spines, and flowers showy, with numerous perianth parts and numerous stamens.

Diagnosis: Fleshy or soft-woody, succulent, green-stemmed, usually armed shrubs to small trees; leaves in ours absent, or present as fleshy points on new growth; specialized, axillary, cushion-like bud areas (= areoles) usually bearing spines and sometimes barbed hairs or bristles (= glochids); flowers solitary or crowded, sessile, closed at night, often showy; sepal-like perianth parts 5 or more, grading into the many, thin-textured petal-like structures, all joined at base to form a cup or tube (= hypanthium) on summit of the thick, pedicel-like, inferior ovary; stamens many; fruit a dry or fleshy berry.


Notes: A medium-large (1,400 species in 97 genera) family of stem-succulent xerophytes native almost exclusively to the New World, but now widely naturalized; some have become problematic invaders (e.g., Opuntia in Australia); the family includes a number of epiphytes. Xerophytic adaptations include a thick cuticle, large volume to surface ratio, widespread shallow root system (to take in any available rain), crassulacean acid metabolism (CAM photosynthesis —allows night absorption and storage of CO2 thereby reducing water loss through transpiration during the day-Crosswhite 1984), and spines (condense dew and protect from herbivores). Numerous species are utilized as ornamentals and some are endangered due to overcollecting (e.g., “cactus rustling”); cacti are protected by the Convention of International Trade in Endangered Species (CITES) (Barthlott & Hunt 1993). Many species have alkaloids (e.g., Lophophora williamsii (Lem. ex Salm-Dyck) J.M. Coult.-PEYOTE, which contains the hallucinogen, mescaline, and is used in religious ceremonies by Native Americans). Because of their extreme morphological specializations, the taxonomic placement of the Cactaceae has been problematic; however, biochemical and molecular markers indicate a relationship with the Caryophyllidae (e.g., Cactaceae are characterized by betalain pigments like most other members of this subclass-Cronquist and Thorne 1994). A study by Downie and Palmer (1994) suggested the family may be derived from Portulacaceae. On the basis of molecular data, Hershkovitz and Zimmer (1997) also indicated that the family is derived from within the Portulacaceae and that the molecular divergence "between pereskioid cacti and the genus Talinum (Portulacaceae) is less than that between many Portulacaceae genera." The ancestral condition within the family is clearly observable in the small subfamily Pereskioideae composed of leafy shrubs and trees with only slightly succulent stems. Family name conserved from Cactus, a generic name rejected in favor of Mammillaria (Farr et al. 1979). (Greek: cactus, a spiny or prickly plant) (subclass Caryophyllidae).