The Caryophyllidae
Family Overview - The Caryophyllales
Cactaceae - the Cactus Family
Diversity:  As is the case with many flowering plant families that are well marked by distinctive features and easily recognized, genera of the Cactaceae do not show 'clean' delimitations and opinions vary (lumpers vs. splitters) with regard to the number of taxa at various levels.  As treated by the Flora of North America, the family includes from125 to 130 genera with about 1, 800 species; 34 genera and 89 species in the FNA region.

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 21 genera and 103 species, with 56 infraspecific taxa.

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  (Opuntia) 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 (images).  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.

pereskia shoot carr pereskia
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

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18 Feb 2010