Henk Beentje 
Flora of Tropical East Africa [PDF ebook] 
Apocynaceae II

The Flora of Tropical East Africa is a descriptive, extensively illustrated account of the flowering plants and ferns native and naturalized in Kenya, Tanzania, and Uganda, together with information on exotic ornamental and crop plants. At least one species of each genus is illustrated, and the bibliography and synonymy are sufficiently detailed to explain the nomenclature and taxonomic circumscriptions within a broad regional context. This part of the series is the second volume devoted to the Apocynaceae family or dogbane, which includes trees, shrubs, herbs, and lianas.