Ruth Ruberté

A WildIpomoea Species Closely Related to the Sweet Potato

In a brilliant study of certain species of Ipomoea closely related to the sweet potato Ipomoea batatas (L.) Lamn., Nishiyama (1971) claims not only to have found the primitive wild type of 90 chromosomes from which the sweet potato originated, but also to have resynthesized the wild type from a diploid and a tetraploid species. In contrast, in a very careful study of many of the diploid and tetraploid relatives of the sweet potato, Martin and Jones (1972) point out that none of the species so far found resembles the sweet potato enough to be its ancestor. They hypothesize that the described diploid species are closely related to each other, but that the tetraploid species show no close resemblances to each other, to the diploids, or to the sweet potato. Nishiyamas (1971) hypothesis is that the tetraploid progenitor of sweet potato is I. littoralis Blume, a species that when grown in Mayaguez, Puerto Rico, proved to be equal to what Martin and Jones (1972) have called I. gracilis R. Br. Matuda (1963) and van Oostroom (1953) consider I. littoralis to be a synonym for L gracilis. As they point out, the species has forms with cordate leaves as well as with lobed leaves. Nevertheless, Nishiyama apparently recognizes other differences, because he treats L littoralis and L gracilis as separate species (1971).