Distribution:  With one exception, a few epiphytic species of the pencil cactus (Rhipsalis, ca. 35 species) that are found in Africa and Madagascar, the Family is limited to the Americas, mostly in xeric areas.  The Texas flora includes 19 genera and about 100 species.

Floral structure:

Significant features:  The most conspicuous markers for this family relate to adaptation for life in a xeric environment.  Xerophytic features include reduced, fugacious leaves with transfer of photosynthetic function to the stem which also serves to store water - they are (mostly) stem succulents.  Taxa producing massive or 'arborescent' stems, such as the Carnegiea gigantea pictured to the left) are herbs (no seconary xylem) with reticulate, lignified vascular systems that provide a supportive frame.  Since water is in short supply in their habitat, protection of the resource has been established by clusters of spines (developmentally modified lateral buds) at each node, these are known as areoles (image).  Cacti, especially those lacking areoles, also use chemical deterrents (alkaloids - Lophophora williamsii - Peyote Cactus of West Texas).  Cactus flowers show classic archaic features (actinomorphic, often solitary, polypetalous, numerous stamens) and epigyny which, in this family, has involved stem tissue.

  Local 'prickly pear', Opuntia lindheimeri, flower showing archaic (similar to Magnoliidae) features
 
 
 
 
 

Opuntia - with stem tissue and areoles evident beyond the pericarp
 
 

Pereskia - a primtive cactus (with photosynthetic leaves) from Argentina
 
 

  Pereskia - typical cactus flower (image from the University of Hawaii)

More information on the Cactaceae