Benson rejected the name Opuntia engelmannii, viewing it as Opuntia phaeacantha var. discata, and preserved Opuntia lindheimeri as a good species.
Hunt currently recognizes only the species Opuntia engelmannii (with Opuntia lindheimeri dissolved into it).
Our presentation is largely in alignment with Powell (i.e. the view of Parfitt & Pinkava 1988 Madroño 35: 342-349):
Our one point of divergence is viewing linguiformis simply as a form rather than a variety of Opuntia engelmannii var. lindheimeri.