I have been working on many herbarium specimens of Solanum usambarense, but I was not sure whether it was the same species as Solanum anguivi or whether it was really different. Today we searched for Solanum usambarense and I was finally able to solve this problem. Both species were growing together in the forest understorey of a Prunus africana plantation heavily invaded by Solanum robustum. The two species were consistency different from each other even though they grew together, and I could confirm the things I observed in the herbarium: Solanum usambarense has more flowers, its pedicels are always recurved, and it is more hairy.
Comparing Solanum anguivi and Solanum usambarense, which grew a few meters away from each other.