Sometimes I can’t track down what seems to be the most agreed-upon name for a taxon, and this is one of those times. Depending on the resource, this species is listed under Caralluma retrospiciens, Caralluma acutangula and Desmidorchis retrospiciens. I’ve opted to follow the latest version of The Plant List. Bart Wursten, the photographer, also edited his image titles to Caralluma retrospiciens after originally using Caralluma acutangula, so perhaps he’s been in contact with someone who knows the latest literature.
In Flora of West Tropical Africa, Volume 2, published by the Royal Botanic Gardens, Kew, this species is described as:
An erect sparsely branched greyish-green shrubby succulent, perhaps the largest of the stapeliads, the winged stems indurated on the margins and armed with spreading or reflexed hard teeth; flowers almost black in large globose heads at the tips of the branches.
JSTOR’s Global Plants provides the information above on this page, with many additional photos: Caralluma retrospiciens. Global Plants has also a species page for Caralluma retrospiciens with a more scientific description as well as mention of its native range: Djibouti, Eritrea, Ethiopia, Kenya, Uganda, Saudi Arabia, Somalia, and Yemen. The latter link also includes local common names, which differ by country and indigenous group.
The Kew account notes that this is perhaps the largest of the stapeliads. Plant taxonomists sometimes add additional granularity between the hierarchical ranks of family and genus (and indeed other ranks). To use this as an example, the Apocynaceae or dogbane family contains a subfamily called Asclepiadoideae. The asclepiads strongly (or exactly) mirror the old family Asclepiadaceae (the milkweeds), which thanks to molecular work had been subsumed into the Apocynaceae. Within the subfamily Asclepiadoideae, another division is made: tribes. Stapeliads are members of the tribe Stapeliae. Again, quoting from that link to Wikipedia, here are some features which unite this group:
[Stapeliads] are all to varying degrees stem succulents. Many of the species resemble cacti, though are not closely related, as an example of convergent evolution. The stems are often angular, mostly four-angled in cross-section, but in some species there are six or more…The leaves are in most species reduced to rudiments, sometimes hardened and thorn-like, arranged on bumps or tubercles on the angles. Some species, however, still have recognizable leaves…Stapeliads are most abundant in warm, dry climates…Stapeliads are often regarded as a climax group within the family because of their often structurally complex flowers. Certain aspects of these reproductive parts mirror the pollination systems in the Orchid family and represent a case of parallel evolution though both groups are quite unrelated and have developed similar, though not identical means to achieve the ultimate goal of pollination and therefore reproduction. Most stapeliads use flies as pollinators, that are attracted to odours resembling dung or rotting meat, emanating from the flowers.