荸荠 bi qi

Andropogon dulcis N. L. Burman, Fl. Indica, 219. 1768; Eleocharis equisetina J. Presl & C. Presl; E. plantaginea (Retzius) Roemer & Schultes; E. plantagineiformis Tang & F. T. Wang; E. tuberosa Schultes; Scirpus plantagineus Retzius; S. tuberosus Roxburgh (1819), not Desfontaines (1798).

Perennials. Stolons slender, often terminated by a tuber. Culms erect, grayish green, tufted, 15-60 cm tall, 1.5-3 mm thick, cylindric, smooth, glabrous, surface with transverse septa, nodes evident when dry. Leaf sheaths 2 or 3, greenish yellow, purplish red, or brown, 2-20 cm, mouth obliquely truncate, apex acute. Spikelet pale green, cylindric, 1.5-4 cm × 6-7 mm, many flowered. Basal 2 glumes empty, amplexicaul for whole spikelet base; fertile glumes grayish green, laxly imbricate, broadly oblong to ovate-oblong, 3-5 × 2.5-3.5(-4) mm, subleathery, pale brown puncticulate and finely striate, margin pale yellow and membranous, apex obtuse. Perianth bristles 7, ca. 1.5 × as long as nutlet, retrorsely spinulose. Stigmas 3. Nutlet brown when mature, broadly obovoid, ca. 2.5 × 1.8 mm, biconvex, essentially smooth but faintly and finely cancellate with hexagonal to oblong hexagonal epidermal cells, apex not constricted but with an annular thickening; persistent style base triangular-attenuate, flattened, not spongy, base ca. 1/2 as wide as nutlet. Fl. and fr. May-Oct. 2n = 38, ca. 108.

Field margins, lake margins, commonly cultivated; near sea level to 1500 m. Fujian, Guangdong, Guangxi, Hainan, Hubei, W Hunan, Jiangsu, Taiwan [India, Indonesia, Japan, Korea, Malaysia, Myanmar, Nepal, Pakistan, Papua New Guinea, Philippines, Sri Lanka, Thailand, Vietnam; tropical Africa, N Australia, Indian Ocean islands, Madagascar, Pacific islands].

The tuber (water chestnut) is eaten.

Although originating in the Old World tropics, because this species is commonly cultivated for its tubers, the actual distribution is uncertain. As a cultivated plant, it is grown throughout most of China.