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.
The most conspicuous markers for this family relate to adaptation for
xeric environment. Xerophytic
features include reduced, fugacious
of photosynthetic function to the stem which also
serves to store water - they are (mostly) stem
succulents. Taxa producing massive or 'arborescent'
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
is in short supply in their habitat, protection of the resource has
established by clusters of spines
modified lateral buds) at each node, these are known as areoles (images).
Cacti, especially those lacking areoles,
deterrents (alkaloids - Lophophora
williamsii - Peyote Cactus of West Texas). Cactus
show classic archaic features (actinomorphic, often solitary,
numerous stamens) and epigyny which, in this family, has involved stem
|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)|