At www.flora.sanbi.org one sees that there are 1700 mesemb or Aizoaceae species worldwide, classified into 127 genera. To complicate matters, there are today about 6000 old mesemb species names around in the literature! These include many synonyms as well as the old, discarded names that still persist all over the botanical and popular literature. No wonder the confusion arising from identification discussions!
Fortunately there is an official system in place, serviced by an international authority of which South African botanists form an organized part. The interested amateur does well by learning the binomial naming system, like a proper name and surname system.
The overall taxonomic structure started by Linnaeus in the 18th century takes more effort, also holding rewards. Still more daunting are the current conventions for naming and updating names and groupings every time the authorities decide to recognise new knowledge in a name.