•The water-yam, Dioscorea
alata, another cultigen of SE Asian origin, is cultivated
throughout West Africa
and sporadically in East Africa and Ethiopia, as well as on Madagascar.
•The water-yam has a long dormancy period (Martin 1976), a feature that makes it an
ideal plant to
transport on long ocean voyages, as it avoids the necessity of keeping a plant
alive while en route. This must have been an important factor in its choice as a major staple in
Oceania.
•Chevalier (1936:522 ff.) concluded that the water-yam was long-established in West Africa, although he offers no hypothesis about the
route of its
introduction.
•Timitimi (1970) shows that the Kolokuma recognise eighteen cvs. of D. alata while Raponda-Walker & Sillans (1961:150)
list three major
subgroups and numerous other varieties grown in Gabon. If this is compared with
other tubers
introduced by the Portuguese, such as the fertile and easily bred sweet potato, such a shallow time-depth seems unlikely.
•