areas in Tanzania and possibly other regions of East Africa where 

 climatic conditions are suitable. 



Outside Africa, the West African yams are very sporadically 

 distributed, and their occurrence in particular regions appears to 

 be due to historical accident. In the Caribbean, for example, the 

 pattern of cultivation is not rational; whereas very good cultivars 

 of D. rotundata are important in Jamaica, Puerto Rico, and the 

 French West Indies, they are virtually unknown on other islands. 

 The African yams are seldom seen in Southeast Asia or on the 

 islands of the Pacific except in New Caledonia, where they were 

 introduced by the French. In several areas of Brazil they have 

 also become important. 



Wide distribution of the West African yams appears desirable. 

 Because of their adaptability to areas somewhat drier than those 

 where D. alata is grown and because of the earliness of most 

 cultivars, the African species, especially D. rotundata, should be 

 able to fill a special niche where other species of yams are less 

 successful. 



BOTANY 



Classification 



Both D. rotundata and D. cayenensis belong to the section 

 Enantiophyllum, the most important section of the genus. The 

 section is known only in the Old World. Tubers of this section are 

 usually vertical, and the leaves are simple. In addition to the two 

 species under consideration here, the section includes the Asian 

 species D. alata and D. opposita Thunb., and the important African 

 species D. abyssinica Hockst., D. colocasiifolia Pax, D. lecardi de 

 Wild., D. liehrechtsiana, D, mangenotiana Miege, D. praehensilis 

 Benth., and several others, some of which are used for food 

 under special circumstances. Both the Asian species, about 50, 

 and the African have been described by Burkill 5). 



In common with other yams, the species mentioned above 

 belong to the family Dioscoreaceae, of which Dioscorea is the 

 principal genus. The family is usually classified among the mono- 

 cotyledons, although some evidence of a second cotyledon has 

 been found (16). The family is characterized by rhizomes, usually 

 reduced to a nodeless structure, the tuber. Male and female 

 flowers, usually on separate plants, are small and often incon- 

 spicuous. The floral pattern is based on sets of three. 



To some, D. rotundata and D. cayenensis are the same species, 

 whereas to others the former is a botanical variety of the latter. 

 The taxonomic controversy is far from resolution. Characteristics 

 generally attributed to the more clear-cut forms of the two species 

 are given in table 1. Ayensu has found subtle anatomical differ- 



4 



