Plant Ecology and Evolution 147(1): 33-48, doi: 10.5091/plecevo.2014.824
Flower morphological diversity in Aframomum (Zingiberaceae) from Africa – the importance of distinct floral types with presumably specific pollinator associations, differential habitat adaptations and allopatry in speciation and species maintenance
expand article infoAlexandra Ley, David J. Harris§
‡ Institut für Geobotanik und Botanischer Garten, Halle, Germany§ Royal Botanic Garden Edinburgh, Edinburgh, United Kingdom
Open Access
Background and aimsAframomum (61 species) is a tropical African genus of the family Zingiberaceae (~53 genera) of perennial rhizomatous herbs most often growing in the forest understorey. The family Zingiberaceae is known for a high diversity in floral morphology and pollination systems in Asia, however, almost nothing is known in Africa. In this study we explore the floral diversity in Aframomum and the potential of this diversity to mediate isolation as driving force for species divergence and maintenance in Aframomum in contrast to other postulated drivers such as allopatry and habitat differentiation. Methods and key results – We conducted a survey of floral morphology in eighteen species across the genus identifying five floral types and their morphological adaptations to different pollinators. Another 38 species were subsequently attributed to one of these types based on monographic descriptions and photos. Differences in floral types were based on slight changes in the relative length and position of dorsal petal, labellum and the complex of anther and style. The mapping of floral types onto an existing phylogenetic tree indicated their repeated independent evolution. The preponderate presence of one rather uniform floral type in about 60% of all taxa (Trumpet type) suggests a low number of inferred pollinator shifts (30%). Conclusion – The low number of inferred shifts in floral types alone cannot alone explain the diversification of this genus. Here the often small non-overlapping distribution ranges and narrow habitat preferences of species and the phylogenetic distance of sympatric species suggest the additional importance of allopatry and phylogenetic incompatibility as isolation mechanisms in maintaining species boundaries in this genus.