When I collated data on the Malviflora of South Africa a while back I wasn't able to find much information of the flora of Angola. Since then I found a copy of W.P. Hiern's Catalog of Welwitsch's African Plants at Internet Archive. Over the weekend I've extracted the data from there, and integrated it into the Malviflora of South Africa pages.
This doubled the number of species in Angola per my records. While the list may well still be incomplete it is comparable in size with that for other South African countries, so it should at least be a reasonable representation of the diversity.
Google Search was used to evaluate the names used by Hiern for current validity. It turns out that Aluka has a considerable amount of data on the synonymies of African Plants (from the Floras of West Tropical and East Tropical Africa). It looks as if I'll have to dig into this someday and update my nomenclatural databases. The Flora of East Tropical Africa also has extralimital ranges, so I may be able to identify further Angolan species from there.