1	Stem twining to right; often at least some leaves opposite, always simple, though sometimes with enlarged basal lobes		8 Dioscorea sect. Enantiophyllum
+	Stem twining to left; leaves alternate, rarely ± whorled toward base of stem, sometimes palmately compound or lobed.		(2)
2 (1)	Stem and leaves with T-shaped hairs .		3 Dioscorea sect. Combilium
+	Stem and leaves without T-shaped hairs.		(3)
3 (2)	Leaves nearly all palmately 3- or more foliolate (rarely with apical leaves simple); rootstock a tuber or group of tubers; seeds inserted near apex of capsule with wing pointing toward capsule base.		(4)
+	Leaves mostly simple; if compound leaves present then rootstock a horizontally spreading rhizome, basal leaves sometimes simple, and seeds inserted near middle of capsule and winged all round.		(5)
4 (3)	Leaflets often more than 3, pinnately veined with 1 midvein; male flowers with 3 stamens and 3 staminodes		6 Dioscorea sect. Botryosicyos
+	Leaflets always 3, prominently palmately veined from base; male flowers with 6 stamens		7 Dioscorea sect. Lasiophyton
5 (3)	Perianth lobes narrowly oblong; seeds inserted near apex of capsule with wing pointing toward capsule base; petiole base with a pair of stipulelike, blunt, fleshy swellings (shrinking considerably on drying)		5 Dioscorea sect. Opsophyton
+	Perianth lobes usually elliptic to ovate; seeds inserted near base of capsule with wing pointing toward capsule apex, or inserted near middle and winged all round; petiole base without stipulelike swellings, though sometimes with small prickles at nodes.		(6)
6 (5)	Male flowers always solitary along inflorescence axis; capsule not reflexed, distinctly wider than long		2 Dioscorea sect. Stenocorea
+	Male flowers in sessile clusters or pedunculate cymules at least toward base of inflorescence; capsule reflexed, about as long as to distinctly longer than wide.		(7)
7 (6)	Rootstock a horizontally spreading rhizome; leaf blade margin sometimes undulate to deeply lobed; male flowers usually in sessile clusters (in cymules in D. nipponica var. rosthornii); indumentum short and stiff when present; capsule always with straight wings; seeds usually inserted near middle of capsule and winged all round, rarely inserted near base with wing pointing toward capsule apex (and then leaf blade with distinctly toothed to 4- or more lobed margin)		1 Dioscorea sect. Stenophora
+	Rootstock of vertical tubers; leaf blade margin always entire; male flowers usually in pedunculate cymules (sessile in D. tentaculigera); indumentum often softly pubescent when present (very shortly papillose in D. tentaculigera); capsule often with undulate wings; seeds inserted near base of capsule with wing pointing toward capsule apex		4 Dioscorea sect. Shannicorea