No, it’s not an Opuntia (prickly pear) and it’s not exotic!
Codon royenii, here a big-leaved, young plant among the rocky hills of the Goegap Nature Reserve grows a substantial taproot, living in the arid sands of its often rocky habitat.
Sometimes only an annual, these mostly short to longer-lived perennial herbs are profusely spiny in the majority of plant parts and succulent in its dark green leaves.
There are only two species in the Codon genus; the other one, C. schenckii, bearing shallow flower cups (Le Roux, et al, 2005; Leistner, (Ed.), 2000; Eliovson, 1990; iNaturalist; Wikipedia; http://pza.sanbi.org).