South African Foxglove
I'm not a collector of South African plants, but a wonderful and underrated South African native is Ceratotheca triloba, a.k.a. South African Foxglove. Ceratotheca triloba is an easy, drought tolerant annual in the sesame family. I believe it's technically a perennial but in my area (zone 7a) it isn't hardy; it does reseed itself fairly reliably in my garden.
Here is a link that might be useful: Ceratotheca triloba