A revision of Corynanthe and Pausinystalia (African Rubiaceae-Coptosapelteae)

Abstract

The genera Corynanthe and Pausinystalia are an easily recognizable group within the tribe Coptosapelteae because the corolla lobes are provided with a distinct spherical, club-shaped or linear appendage. In the past the delimitation of the species and the 1–3 genera in the literature has been problematical. A short revision of the group is undertaken, based mainly on a study of Central African herbarium specimens. The morphological features of the group are reviewed and documented. Stipules were commonly found to have interlocking vernation; this type of ptyxis has not yet been reported from the Rubiaceae. Characters and their states are coded for a numerical phenetic and cladistic analysis of the relationships among the species. Our formal analyses corroborate the view that two genera can be recognized, Corynanthe (characterized by exserted style and anthers, undivided stigma and mainly loculicidal capsule; three species) and Pausinystalia (characterized by style and anthers included in the corolla tube, a bilobed stigma and predominantly septicidal capsule; five species). The entire group probably evolved from a Corynanthe-like ancestor; a drastic shift in flower biology, viz. the loss of secondary pollen presentation, probably correlated with adaptations to another pollinator which may have caused the divergence between the two genera. These show the characteristic distribution pattern of strict rain forest groups in Africa, except that they are missing from the lowland forests of the Zaire Basin. The species are concentrated around the known forest refugia of the quaternary glaciation: only C. pachyceras is distributed in almost the whole rain forest area. A formal taxonomic treatment (with key to species) of the two genera is given; a key to the genera of the Coptosapelteae of the African continent is also included. The examination of the isotypes of forgotten names described by the Berlin school revealed three new synonyms. Pausinystalia angolensis described from Cabinda (Angola) by Wernham is proved to be synonymous with P. macroceras. A few other taxonomic changes are made. Pausinystalia ituriense De Wild, is reduced to a subspecies of P. lane-poolei (Hutch.) Hutch, ex Lane-Poole; P. brachylhyrsum (K. Schum.) W. Brandt is recognized again (instead of being reduced to a form of P. macroceras (K Schum.) Pierre ex Beille), P. talbotii Wernham is maintained in Pausinystalia, and not transferred to Coiynanthe, as recently suggested.