Opuntiacespitosa is a prickly pear in the O.humifusa group of cacti (O.humifusa s.l.). O.cespitosa resembles O.humifusa and has long been overlooked by botanists because it was considered synonymous with that species. O.cespitosa also has similarities with the western species, O.macrorhiza.
O.cespitosa cladodes generally appear glaucous-gray. Cladodes have 0-2 spines that are either both erect or both deflexed. Only centrals are produced. O.cespitosa does not have strongly retrorsely-barbed spines, which are common in the related O.mesacantha. The spines of O.cespitosa place it in contrast with O.humifusa, which lacks spines. Typically, the chains of cladodes are parallel to the ground surface. As with related plants (i.e., O.humifusa s.l.), the cladodes become wrinkled in fall.
O.cespitosa has yellow flowers with red centers. Filaments are yellow and anthers are pale. The style is white and the stigma is white or pale yellow. The fruit is clavate.
O.cespitosa is tetraploid.
O.cespitosa is the most common Opuntia species in the eastern states though it has traditionally been subsumed into O.humifusa and was not noticed. It is present in multiple eastern, southern, and midwestern states including AL, AR, CT, GA, IL, IN, MA, MD, MI, MO, MS, NY, OH, VA and WV. It is the only Opuntia that occurs in eastern Canada (far southern Ontario). Recent work by Paul D. Adanick shows that this Opuntia occurs in many locations in TN and KY but that it may not be numerous at any specific location. It is often found in rocky situations but also occurs in dry soils.
Vegetatively, it is most similar to Opuntiamesacantha ssp. mesacantha, from which this allopolyploid may be partially derived, although floral features are quite different, and O.cespitosa does not have the strongly retrorsely-barbed spines common in O.mesacantha. This species also can be confused with certain forms of O.macrorhiza, another putative parent of O.cespitosa; both species have yellow inner tepals basally tinged red adaxially.