Diversity of wild yams (Dioscorea spp., Dioscoreaceae) collected in continental Africa

Plant genetic resources, especially crop wild relatives like wild yams, are under high risks of extinction due to habitat loss, climate change, unacceptable collection practices, shifting cultivation practice and over-exploitation. To contribute to their conservation, the diversity of wild yams (Dioscorea spp.) collected in continental Africa was analyzed. Specimens from Herbaria (B, BR, K, P, WAG and YA), databases, literature and actual collection from Cameroon were considered. The collection localities were georeferenced and projected to Lambert azimuthal equal-area projection. Spatial analyses of sampling and diversity were conducted at three different resolutions: 50 9 50-, 100 9 100- and 150 9 150-km sized grid cells. Four thousand and eighty-seven specimens, collected in 2895 localities, were inventoried and grouped into 55 taxa including 43 species, five subspecies, four varieties and seven morpho-species. The genus Dioscorea occurred in fifteen out of the eighteen phytochoria recognized on African mainland. The Guineo-Congolian regional centre of endemism was the most sampled and the richest phytochorion with 28 taxa. In terms of floristic composition, the Sudanian regional centre of endemism and the Guinea-Congolia/Sudania regional transition zone were the most similar (similarity coefficient SCi = 0.84). Globally, the most diversified grid cells were located in Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin, Nigeria, Cameroon, Gabon, Equatorial Guinea, CAR, Congo, DRC, Tanzania and Malawi. In terms of phytogeography, they were found in two regional centres of endemism (Guineo-Congolian and Zambezian), two regional transition zones (Guinea-Congolia/Zambezia and GuineaCongolia/ Sudania) and one regional mosaic (Zanzibar-Inhambane). These areas could therefore be considered as potential sites for in situ conservation of wild yams in continental Africa.