Abstract
A taxonomic revision of the African genera of Costaceae (Costus and Paracostus) is given. Within the genus Costus 24 species are recognized, 8 of which are here described as new and one is given a new name. Included are chapters on the history of the taxonomy of the family, morphology, flower biology, pollination, dispersal, distribution, ecology, phylogeny and molecular studies and conservation. The species treatments include descriptions, full synonymy, geographical and ecological notes and taxonomic notes. For all species distribution maps are provided. A complete identification list with all exsiccatae studied and an index to scientific names is included at the end.
Highlights
In Africa, the family of Costaceae comprises two genera: Paracostus and Costus
The genus Costus is widespread in tropical Africa and tropical America, with dispersal from a basal African grade likely leading to the Neotropical radiation (Specht & Stevenson 2006, Salzman et al 2015)
The genus Costus is represented in Africa by 24 species, 8 of which are described as new in this monograph
Summary
In Africa, the family of Costaceae comprises two genera: Paracostus and Costus. The genus Costus is widespread in tropical Africa and tropical America, with dispersal from a basal African grade likely leading to the Neotropical radiation (Specht & Stevenson 2006, Salzman et al 2015). Bracts can be coloured green, red or brownish Their texture is either membranous (C. macranthus, C. spectabilis, Paracostus englerianus), chartaceous (C. acutissimus, C. fenestralis, C. gabonensis, C. lateriflorus, C. ligularis, C. lilaceus, C. loangensis, C. tappenbeckianus) or most commonly coriaceous. The number of calli present and their place in the inflorescence can be quite different: in 5 species bracts, bracteoles and calyx lobes all develop calli, whereas in 3 species no calli were found at all (C. acutissimus, C. macranthus, Paracostus englerianus). The nectar guide is a yellow to yellow-orange blotch of a contrasting colour in the centre of the inner side of the labellum It is present in the flowers of almost all species, except C. ligularis and not distinct in those with completely yellow flowers (C. ga bonensis, C. giganteus, C. gracillimus, C. lateriflorus, C. macranthus, C. spectabilis). The hairs present at the base of the inner side of the labellum around the throat in several species could be the source of this scent and/or could act to facilitate scent volatilization
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