Cylindropuntia is the cholla (choy’-ya) genus. Chollas were formerly treated as a subgenus of Opuntia but have now been separated based on their cylindrical stems and other characteristics. They are one of 3 major opuntiad groups in the US. Though they appear similar, chollas are distinct from the cylindrical Opuntia relatives of South America (Austrocylindropuntia), just as they are distinct from the genus, Grusonia.
Anderson (The Cactus Family, 2001) recognizes 33 cholla species in MX, the US, and the Caribbean, including some putative hybrids (or hybrid-like species) (e.g., C. multigeniculata).
Chollas have jointed stems like opuntias do, but they have papery sheaths on their spines–a feature lacking in opuntias. The plants are typically much branched and make shrubs (eg, C. ramosissima) or larger, almost tree-like plants (eg, C. acanthocarpa).
Chollas are especially common in parts of NM, AZ, CA, and MX. Some species even occur in infrequently in CO, UT, and OK. C. imbricata reaches into southwestern KS. They may be dominant plants that provide food and cover for birds and mammals, or they may be a component of the coastal chapparal. In some locations they are rare. A particularly strong treatment of the genus may be found at CactiGuide.com.