Engelmann & J. M. Bigelow, Proceedings of the American Academy of Arts and Sciences 3: 293, 1856 
Isolectoype; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium (submitted as O. aff polyacantha); Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium (submitted as O. polyacantha); Herbarium (submitted as O. polyacantha); Herbarium (submitted as O. polyacantha); Drawing (Britton and Rose, v1 1919, plate XV)
What is Opuntia tortispina?
Opuntia tortispina is a prickly pear cactus that has been confused with O. cymochila, O. mackensenii, O. phaeacantha and other, small opuntias. O. tortispina may grow alongside the other prickly pears, but it is distinct.
From Powell and Weedin:
O. tortispina is often spinier appearing than other nearby species of Opuntia and is a low, creeping, spreading, and sprawling plant . It seldom exceeds 30 cm tall. The pads are obovate or long obovate about 10-20 cm long and 7-12 cm wide. Areoles over 2/3 of the pads have spines, often 3 to 5 centrals (typically white or tan). Areoles are closer together on O. tortispina than on O. phaeacantha. Pads may/may not have transverse wrinkles in winter; however, unlike O. cymochila the wrinkles smooth out when turgidity returns.
Flowers may be all yellow or may have reddish centers in this prickly pear. The fruits are juicy and obovate to elliptic.
O. tortispina is hexaploid or tetraploid. The two reported ploidy levels may mean that two different taxa exist.
This Opuntia is found in sandy soils in mid-altitude woodlands and grasslands and irregularly in other locations. O. tortispina is found from northern Mexico to Colorado, Arizona, and Texas and perhaps north to Colorado and Kansas. Some botanists consider that O. tortispina is a species of hybrid origin (O. polyacantha and O. macrorhiza). However, such hybridization would have occurred long ago. Nonetheless, it is a stable, self-reproducing and stand-alone species now.