(Haworth) Haworth, Synopsis Plantarum Succulentarum 195, 1812
Opuntia pusilla is a prickly pear cactus of the coastal plains from North Carolina, across northern Florida, to Mississippi. While thought of as a beach cactus, this small prickly pear cactus occurs more than 150 miles inland. O. drummondii may be the correct name for this Opuntia (L Majure, page 167). Some reports (Weniger, 1988) place it on the northern Gulf Coast of Texas also, but the authors have not observed it there. Several other specific epithets have been applied to this smallest of the southeastern opuntias including tracyi, and pes-corvi. Perhaps these are synonyms or perhaps they are discrete taxa yet to be sorted out. See the Cytogeography of the humifusa clade of Opuntia.
The stems of this prickly pear cactus are purplish-red under stress, flattened, elliptic to linear, sometimes subcylindric (to subspheric), 2.5-5(-8) × 1.2-2.5 cm. The stem segments are fragile and detach easily. Spines (0)1-2(-4) per areole are restricted the the distal half of the areoles, but some areoles may have no spines. Spines are porrect to spreading, terete and 20(30) mm. The flowers of this Opuntia are completely yellow. Fruits become red-purple and are barrel shaped. Seeds are tan, subcircular, flattened, and 4 to 6 mm in diameter with a slight girdle.
O. pusilla has been reported to be diploid, triploid, and tetraploid. These ploidies indicate that there are different, but similar-appearing taxa, or they may may only represent ploidy differences within a single taxon. All are treated as a single taxon herein. See the original description.