A Taxonomic Study on Dioscorea of Taiwan － Dioscorea alata
山羊百科，林文智老師的植物、山岳、攝影紀錄
- Chun Kuei Liao chunkuei.liao@gmail.com 2000/06
1. Dioscorea alata L. Sp. Pl. 1033. 1753; Hayata, Ic. Pl. Form. 10: 42, f. 22. 1921; Knuth in Engl. Pflanzenr. 87(4-43):265. 1924; Yamamoto, Suppl. Icon. 3:5. 1927; Sasaki, List Pl. Form. 113. 1928; Prain & Burkill in Ann. Bot. Gard. Callcutta 14(2):302. 1939, pl.123. 1938; Liu, T. S. & T. C. Huang, Bot. Bull. Acad. Sin. 3(2):133. 1962 & Bot. Acad. Sin., Icon. Corm. Sin. 5:568, f.7965. 1976; Liu, T. S. & T. C. Huang in Fl. Taiwan 5:100. 1978; Ting, C. T., M. C. Chang & P. P. Ling. in Fl. China 16(1):117, f.37. 1985.
－Dioscorea alata L. var. prupurea (Roxb.) Pouch. in Bull. Econ. Indo. China n.s. 8:117. 1950; Liu, T. S. & T. C. Huang in Bot. Bull. Acad. Sin. 3(2):133. 1962; Liu, T. S. & T.C. Huang. in Fl. Taiwan 5:100. 1978.
－Dioscorea prupurea Roxb., Fl. Ind. 3:799. 1832.
HABIT DESCRIBE
A glabrous, scandent vine from annual tuber, up to 15 m long; underground tubers polymorphous, mainly cylindrical, cylindroid or globose, occasionally branched or compressed, up to 1 m long; outer epidermis brown to black, some cultivar’s subepidermis purple; flesh white, ivory or purple, edible, never poisonous; aerial stems dextrorse, herbaceous, branched, green or purple, or brown near the base, occasionally prickly or warty toward the base, quadrangular in cross-section, 2-3 mm thick, with 4-longitudinal ridges which enlarged with undulate-wrinkled, membranous green or purple wings; wing 1-2 mm broad, sometimes inconspicuous; aerial tubers axillary, cylindrical or globose, 3-5 cm long, 1.5-2 cm in diameter, yellow-green, dark-brown or purple, somtimes rooting when on stem. Leaves opposite, or alternate in the juvenile or near the base of stem, chartaceous, glabrous, oblong-triangular, oblong-ovate or oblong -cordate, 8-17(-31) cm long, 6-12(-15) cm wide, acuminate or short-caudate at apex, entire at margin, cordate or auriculate or subhastate at base, smooth on both surfaces; nerves 7-9, prominent on both surfaces; veinlets fine and prominent, bright green at upper surface, yellow-green at lower surface; petioles twisted and dilated at base, sulcate above, 2- or 4-winged, wrinkled and extending to stem, 4-10(-15) cm long, 1-5 mm thick.
Staminate inflorescence axillary, spicate, 1-2 together, or compound to narrowly paniculiform, up to 30 cm long; spikes with upward of 20 flowers, 1.5-2 cm long, with a pair opposite ensiform bracts; rachis greenish, rigid, with 2 longitudinal ridges which narrowly winged at base. Male flowers alternate on the short and zigzag rachis, globose, ca. 1.5 mm in diameter, glabrous, 2-bracted; outer bract orbicular, ca. 1.2 mm long, ca. 1 mm wide, acuminate at apex; inner bract obovate, ca. 1 mm long, ca. 0.9 mm wide, acute at apex, round at base, yellow-green; perianths 6, yellow; outer 3 perianths elliptic-ovate, ca.1.8 mm long, ca.1.1 mm wide, obtuse and thickened at apex; inner 3 perianths spatulate or obovate, ca. 1.3 mm long, ca. 0.8 mm wide; stamens 6, subequal, shorter than perianths, filaments terete , ca.0.4 mm long, anthers oblong, ca.1.7 mm long, ca.0.8 mm wide, dorsifixed, longitudinally dehiscent; pistillodium rudimentary, conicus, ca.0.2 mm tall, stigmatiform 3-lobed. Pistillate inflorescence racemose, axillary, solitary or paired, decurved, rigid, up to 60 cm long, with ca. 20 flowers remotely arranged; rachis angled or narrowly winged at base. Female flowers glabrous, green, ca. 8 mm long, ca. 3-5 mm wide, with 2 basal bracts; pedicel ca. 1-2 mm long; perianth segments 6; outer 3 perianth segments ovate, short-acuminate at base; inner perianth segments obovate, thick; staminodia 6; ovary inferior, 3-celled; ovules 2 in each cell; stigmas 3, 2-cleft at apex. Fruit capsulate, pendulous, brownish, obovate, ca. 2.5 cm long, ca. 1.5 cm wide, tripterous, slightly retuse at apex, obtuse at base, rigid; stipe 2-3 mm long. Seeds 2 in each cell, orbicular, with broadly membranous wing around.
This species is distributed in south-east Asia,and spread to India, Malaysia, Indoesia, Philippines, and the eastern portion of south-east Asia, included Taiwain, and has been cultivated for a long time in Taiwan.
It is flowering from September to October, and fruting in November. Most cultivars do not normally flower.
SPECIMENS EXAMINED
SPECIMENS EXAMINED. Taipei City: Pei-t’ou, Y. Shimada, s.n. in 1914 (TAI); Yangminshan (Sozan), Y. Yamamoto s.n. in 1938(TAI 30756); cult. in TFRI, T. C. Huang s.n. in 1960(TAI 30748, 30750, 30747). Taipei Hsien: Shinments’un, C. K. Liao 985; P’inglin, C. K. Liao 995. Tainan Hsien: Liuchia’ts’un, C. K. Liao 986. Kaohsiung Hsien: Ch’ishan, T. Kawakami & U. Mori s.n. in 1907(TAI 49, 6203, 6204, 30758); Liukei, C. E. Chang 19232 (PPI); Meinung, C. K. Liao 992. Pingtung Hsien: Saichia, C. K. Liao 875, 980, 994; Ts’aoputs’un, C. K. Liao 988; T’aiwu, C. K. LIao 1126. Lanyu: S. Sasaki s.n. in 1926 (TAI 30806, 30751); Y. L. Chung 556 (PPI); C. K. Liao 765,993. Ilan Hsien: Ta-t’ung, S. Suzuki 4916 (TAI); Chinyuehts’un(Ryohen & Mohen), S. Suzuki 6035(TAI).
