This common "prickly pear" mostly occurs on base-rich clayey or calcareous soils in midwestern to east-central states, including Ky. (However, it is curiously rare to absent here in the Eden Shale Hills.) The name cespitosa is based on Majure's recent revision (2007; Majure & Ervin 2008; Majure et al. 2012; Majure et al. 2017). In contrast, typical humifusa occurs mostly on non-calcareous soils, mostly in mid-Atlantic coastal states. However, these edaphic associations are not strict; many exceptions are known. Both taxa are tetraploids (2n = 44), apparently derived from diploids further south, where several diploid segregates have been described, especially in coastal regions (Sm, W, FNA 4). O. cespitosa is locally common along limestone clifftops and in old rocky pastures. Cattle avoid eating the cladodes or "pads", which are potentially nutritious and edible if spines are burnt off (Feugang et al. 2006); however, squirrels will occasionally nibble on them (D. Dourson, pers. comm.). Apparently adapted to disturbance from large herbivores, the species may have spread locally within open areas through dispersal of fruit by various mammals, birds (especially turkies) and ants; also pieces of stem might disperse on fur of larger herbivores (Majure et al. 2017) or on farm machinery. Records of Opuntia from HARL,and PIKE represent humifusa sensu stricto; as detailed under that name. See also notes under mesacantha. Remarkably, Rafinesque (1830, p. 216) had reported these same three species of Opuntia from Ky. during 1820-1830: mesacantha, cespitosa and humifusa. A more western species, O. tortispina Engelm. & Bigelow, was reported from Ky. by F, but probably in error. O. tortispina is a variable hexaploid with probable hybrid origin. It has been combined with the more widespread western tetraploid, O. macrorhiza Engelm., or otherwise interpreted (Cr, J, FNA 4). Distinction of the macrorhiza complex from the common eastern Opuntias has been based partly on their tendency to have more spines per areole (up to 6 versus 3), and on the configuration of spines (Y, W, Majure et al. 2017). There is no evidence that such plants occur in Ky.