^{(Photograph = Cyrnopuntia parishii, near Searchlight, NV)}

Introduction

The plants we  think of as Corynopuntia, were not always so easy to label. They have been placed in Opuntia and then Grusonia. At one point it was thought the might belong in the genus Cylindropuntia. Before that they were in the genus Opuntia.

The Details

Grusonia bradtiana is apparently the only real Grusonia, and Micropuntia pulchella has been pulled out of the Grusonia genus. Other plants such as G. aggeria, G. clavata, G. parishii are placed in the genus Corynopuntia now. Plants in Corynopuntia have always differed from supposed close relatives in various ways. In fact, the name Corynopuntia was proposed for the group of plants as far back as 1935 (Backeberg C, FM Knuth 1935 Kaktus-ABC. Gyldendals, Copenhagen).

However, there  was much uncertainty over the years. It is only in the past dozen years that Corynopuntia as been recognized as the proper place for many plants formerly in Grusonia. Various studies now support this interpretation, and the New Cactus Lexicon (2006) places the plants in Corynopuntia. However, opuntiad taxonomy changes as new information is obtained. Maybe these plants will have a new genus or maybe they will be returned to Grusonia. Maybe they will be placed somewhere else. Opuntiad taxonomy is a moving target. 

Native Americans used ground up Corynopuntia to treat sores and wounds (Anderson, 2001).