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FOC | Family List | FOC Vol. 24 | Dioscoreaceae

1. Dioscorea Linnaeus, Sp. Pl. 2: 1032. 1753.

薯蓣属 shu yu shu

Dioscorea alata

Credit: O. Tellez

Herbs twining. Rootstock rhizomatous or tuberous, variable in color, shape, chemical constituents, and depth in ground. Bulblets axillary or absent. Leaves alternate or opposite, petiolate, simple or palmately compound, basal veins 3--9. Flowers unisexual (plants dioecious, rarely monoecious), arranged spirally in axillary, usually elongate spikes or racemes, or in small cymules in ± spikelike thyrses, these often several together, sometimes gathered into a terminal or axillary panicle by reduction of subtending leaves. Male flowers: stamens 6, 3 sometimes reduced to staminodes or absent. Female spikes 3.5--10 cm, few flowered. Female flowers: staminodes 3, 6, or absent. Capsule 3-winged, dehiscent apically at maturity. Seeds with a membranous wing.

More than 600 species: widely distributed in tropical and temperate regions; 52 species (21 endemic, two introduced) in China.

Dioscorea is a genus of great economic value, including important food plants. Several species are widely cultivated in many cultivars (including Dioscorea alata D. esculenta D. japonica and D. polystachya), while other, wild species are valuable famine foods. Other species are sources of drugs both in traditional Chinese and Western medicine (notably D. nipponica and D. zingiberensis which are major sources of steroid precursors).

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

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