Description:

• Perennial plants with variously modified succulent stems, epiphytes, shrubs or trees, often spiny; spines, branches, flowers and often irritant hairs (glochids) arise from usually raised cushions or areoles which may represent axillary buds or condensed side branches
• Leaves usually rudimentary
• Flowers bisexual, regular, rarely irregular, usually showy, solitary or clustered, axillary
• Calyx adnate to ovary and shortly tubular above; lobes often numerous, in several rows, scale-like, foliaceous, or petaloid
• Corolla usually of many petals in several rows, free or connate into a short tube, the outer merging into sepals
• Stamens usually numerous, in several rows, arising in calyx throat, sometimes adnate to base of petals; anthers 2-thecous
• Ovary inferior, 1-locular, with many ovules on 3 or more parietal placentas; style terminal, simple, with as many stigmas as placentas
• Fruit a berry, rarely dry, smooth or ± spiny
• Seeds many, with smooth and shiny or tuberculate, often black testa

Nomenclature:

• Cactaceae
  • Harvey: 479 (1862)
  • Britton & Rose (1919-23)
  • Berger (1929)
  • Backeberg (1958-62)
  • Obermeyer: 144 (1976)
  • IOS Working Party: 65 (1986)
  • IOS Working Party: 85 (1990)
  • Barthlott & Hunt: 161 (1993)

Distribution & Notes:

• Global: Genera 100-150, species ± 2 000, mostly arid, tropical America
• Southern Africa: Genera genera 7 (6 naturalised), species 19 (18 naturalised). Many species cultivated, often naturalised in hot dry regions worldwide; often troublesome invaders. Only Rhipsalis is considered an Old World genus and appears to be indigenous

References:

• BACKEBERG, C. 1958-1962. Die Cactaceae. Gustav Fischer, Jena
• BARTHLOTT, W. & HUNT, D.R. 1993. Cactaceae. In K. Kubitzki, J.G. Rohwer & V. Bittrich, The families and genera of flowering plants 2. Springer-Verlag, Berlin
• BERGER, A. 1929. Kakteen. Ulmer, Stuttgart
• BRITTON, N.L. & ROSE, J.N. 1919-1923. The Cactaceae. Carnegie Institution, Washington
• HARVEY, W.H. 1862. Cactaceae. Flora capensis 2
• IOS WORKING PARTY 1986. The genera of the Cactaceae: towards a new consensus. Bradleya 4
• IOS WORKING PARTY 1990. The genera of Cactaceae: progress towards consensus. Bradleya 8
• OBERMEYER, A.A. 1976. Cactaceae. Flora of southern Africa 22

Resources:

• Key to Cactaceae genera

• Cactaceae genera: