Fitting pieces together - Pterodiscus Hooker (Pedaliaceae) in tropical NE Africa. A case study

The genus Pterodiscus presents difficult taxonomic problems, especially in tropical NE Africa, which are mainly due to: (1) high variability in nearly all characters, albeit the fruit morphology being the most stable character complex; (2) clines arid character introgression, where distribution areas are in contact or overlap; (3) very inadequate type specimens, often not exhibiting the taxonomically important characters, and subsequent incomplete, sometimes even erroneous descriptions. Due to intensified collecting during the two last decades and tire availability of living material and photographs taken in the natural habitat, it has now been possible to clarify the taxonomy of the tropical NE African species and to provide more complete descriptions. The presence of three fruit types that do not agree with the original generic description, necessitates a reconsideration of the concept of Pterodiscus. Pterodiscus in its present circumscription cannot be considered a natural group from a strictly phylogenetic point of view. The genus is a good example of the often irreconcilable conflict between practical (Linnaean) and phylogenetic (monophyletic or cladistic) taxonomy, currently a topic of discussion in the literature.