甘薯 gan shu

Tubers usually 4--10, produced from apical branches of rhizome; cork light yellow, smooth; thorny roots present or absent. Stem twining to left, with T-shaped, soft hairs, proximally prickly, distally so only at nodes. Leaves alternate, simple; petiole 5--8 cm; leaf blade broadly cordate, to 15 × 17 cm, with T-shaped hairs especially abaxially, basal veins 9--13, base cordate, apex acute. Male spike solitary, dense, ca. 15 cm. Male flowers: usually solitary, rarely in cymules of 2--4, sessile or subsessile; bract ovate; perianth shallowly cupular, puberulent, outer lobes broadly lanceolate, ca. 1.8 mm, inner ones slightly shorter than outer; stamens 6, inserted in perianth tube, slightly shorter than perianth lobes. Female spike solitary, pendent, to 40 cm. Capsule very seldom maturing, ca. 3 cm, base truncate, apex slightly emarginate; wings ca. 1.2 cm wide. Seeds inserted near middle of capsule, winged all round. Fl. early summer.

Cultivated. S Guangxi, Hainan, Taiwan [native to India, Malaysia, Papua New Guinea, and Thailand; long cultivated in tropical Asia].

Known to have been cultivated in S China for at least 1700 years. The thornless forms are probably selections from an original, thorny form.