The enantiophyllum clade of dioscorea in Africa: Systematics, distribution and conservation assessment

Abstract

Yams belong to the Dioscorea L. which is by far the largest genus in Dioscoreaceae with over 600 species and the fourth most important tuber crop in economic terms after potatoes, cassava and sweet potatoes. Yams are important food plants in many parts of the world, especially in West Africa, which produces about 93% of the World production. Dioscorea cayennensis and D. rotundata, which are collectively referred to as Guinea yams, are the most important cultivated yams native to Africa. Guinea yams belong to the Enantiophyllum clade which contains species with stems twining to the right. Despite the importance of Guinea yams, their relationship within the clade is poorly understood. In order trace the wild ancestors of the Guinea yams, a phylogenetic analysis based on sequence data from six plastid genes using 46 accessions of Dioscorea containing 12 of the 21 species of Enantiophyllum in Africa was carried out. Results showed that D. baya, D. praehensilis and D. abyssinica are the closest wild relatives of the Guinea yams. I also reconstructed ancestral morphological characters states for the African Dioscorea in the Enantiophyllum clade to understand how characters have evolved over time. It was revealed that morphological character diversity is a product of evolutionary changes. The current and potential impacts of climate change on the habitat distribution of Dioscorea in Africa were also evaluated to establish the actual and potential areas of occurrence for proper conservation planning. Dioscorea cotinifolia, D. praehensilis and D. schimperiana are shown to likely be affected by climate change. An IUCN Red List assessment was also performed to know the threat status and population trend of the wild African Enantiophyllum species of Dioscorea to identify species that needs immediate conservation management. All assessed species are classified as Least Concern (LC).