An Account of Bidens (Compositae: Heliantheae) for Africa

Abstract

Monographs of Coreopsis L. and Bidens L. were published by E. E. Sherff in 1936 and 1937, respectively. Characters and character states used since the time of Linnaeus (1753) to differentiate between these taxa were evaluated in these works. Difficulties in the assignment of taxa from South America and the Pacific Islands to one or the other genus were expressed while the African species were regarded as presenting little or no difficulty. In some cases, however (Sherff 1937: 544545), close resemblances between taxa within these genera were portrayed, e.g. Bidens steppia (Steetz) Sherff was compared with Coreopsis oligoflora Klatt (= Bidens oligoflora (Klatt) Wild). Later studies on African members of Coreopsis L. and Bidens L. (e.g. Wild 1967; Cufodontis 1967; Agnew 1974; Wickens 1976; Mesfin 1984, 1986) indicated that the characters used in separating them are too variable even within a single species. In connection with his studies on Polynesian taxa, Gillett (1975) discussed the taxonomic difficulties caused by the presumed differential characters between Bidens and Coreopsis. A revision of the genus Bidens for NE Tropical Africa was presented by Mesfin (1984a) wherein all taxa from this region which were previously kept in Coreopsis L. were transferred to Bidens L. In a subsequent paper (Mesfin 1986), the morphological basis for the inclusion of African species of Coreopsis L. in Bidens L. was given. The present work is the culmination of the study begun in 1980. It is an attempt towards the presentation of a fuller account of the genus Bidens L. for Africa incorporating into it all taxa that have hitherto been treated within Coreopsis L. For taxa that have recently been revised (cf. Mesfin 1984a, 1984b, 1986) only the revised list of synonymy, the pattern of distribution and the habitat are provided. Only a few selected specimens are provided for each taxon. A separate list of examined specimens is deposited at EA, ETH, K and UPS.