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FOC | Family List | FOC Vol. 24 | Dioscoreaceae | Dioscorea

42. Dioscorea japonica Thunberg in Murray, Syst. Veg., ed. 14. 889. 1784.

日本薯蓣 ri ben shu yu

Tubers vertical, long cylindric, to 3 cm in diam.; cork yellowish brown; transverse section white or yellowish white. Stem twining to right, green, sometimes light purplish red. Bulblets often present. Leaves alternate basally on stem, opposite distally on stem, simple; petiole 1.5--4(--6) cm; leaf blade drying yellowish green to light brownish, broadly ovate basally on stem, usually triangular-lanceolate to linear distally on stem, 3--12(--19) × 1--6(--18) cm, membranous or papery, glabrous, basal veins 5--9, base sagittate or hastate to cordate or ± truncate, margin entire, apex acute to long acuminate. Male spikes 3--5 together, rarely solitary, ± erect or ascending, 2--8 cm; rachis straight, occasionally slightly zigzagged at apex. Male flowers: perianth greenish white or light yellow, lobes purple spotted, ovate or ovate-elliptic, to 2 × 1.5 mm, inner ones smaller than outer; stamens 6. Female spikes solitary or 2 or 3 together, 6--20 cm. Female flowers: staminodes 6. Capsule not reflexed, pale brown with darker, linear freckles, oblate, 1.5--2(--2.5) cm, base truncate, apex emarginate; wings 0.7--1.5(--2) cm wide, margin dark. Seeds inserted near middle of capsule, D-shaped, ca. 1.9 cm (ca. 0.7 cm excluding wing), winged all round. Fl. May--Oct, fr. Jul--Nov.

Mixed forests and margins, scrub forests, herb communities, mountain slopes, valleys, along rivers and streams, roadsides; 100--1200 m. Anhui, Fujian, Guangdong, Guangxi, E and S Guizhou, Hubei, Hunan, Jiangsu, Jiangxi, Sichuan, Taiwan, Zhejiang [Japan, Korea].

1 Stem, petiole, leaf blade veins abaxially, and base of female peduncle minutely puberulent when young   42c var. pilifera
+ Plants glabrous throughout.   (2)
2 (1) Leaf blade triangular-lanceolate or lanceolate to long elliptic, (1--)2--5(--18) cm wide   42a var. japonica
+ Leaf blade lanceolate to linear, 0.7--1.5(--3) cm wide   42b var. oldhamii


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