Ricefield Flatsedge

台灣特有種

Cyperus iria was first recorded in the New World from the southeastern United States in the 1840s.

台灣特有種

Herbs, annual, cespitose. Culms trigonous, (5–)20–60 cm × (0.2–) 0.6–2.4 mm, glabrous. Leaves (1–)3–4, V-shaped, 15–40 cm × 3–6 mm. Inflorescences: spikes 2–5(–8), oblong to ovoid, 2–10 cm × 3–12 mm; rays 4–8, to 11 cm; bracts (4–)5(–7), ascending at 45°, V-shaped, (1.5–)8–30(–50) cm × 1–6 mm; rachilla persistent, wingless (successive floral scales 0.7–0.9 mm apart). Spikelets 10–30, compressed, linear to ellipsoid, 4–20 × 1.5–2.1 mm; floral scales deciduous, (2–)6–26, laterally brown to golden brown, edges clear, medially green, 5-ribbed, outermost ribs more noticeable than others, obovate to nearly orbiculate, 1.3–1.8 × 1.2–1.8 mm, margins emarginate, apex with mucro 0.05–0.12 mm. Flowers: stamens 2(–3); anthers (0.2–)0.3–0.4 mm, connective tips reddish, less than 0.1 mm; styles less than 0.1 mm; stigmas 0.2–0.4 mm. Achenes brown, slightly stipitate, obovoid, 1.2–1.4 × 0.5–0.7 mm, apex apiculate, surfaces puncticulate.

Annual, 20-70 cm, solitary or forming small tussocks. Rhizome small. Stem 2-3 mm diam., trigonous, smooth. Leaves up to equalling stem; sheaths to 20 cm, soft, yellow brown, sometimes with reddish tint, finely brown-dotted, mouth margin straight; ligule 0; blades to more than 30 cm, 2-5 mm wide, flat, keeled, green or greyish green, margins slightly revolute, margins and keel towards the apex scabrous, apex acute, scabrous. Inflorescence a compound anthelodium, 5-20 cm; 4-6 bracts foliose, to more than 25 cm, much longer than inflorescence; primary branches up to 15 cm, rigid; secondary anthelodium 20-50 mm; tertiary anthelodium 20-30 mm; cluster of spikes 10-40 mm, spikate, erect, lax, with c. 40 spikes; spikes 3.5-5 x c. 2 mm, compressed, lax, with 5-20 flowers, glume-like bract c. 1 mm, glume-like prophyll scarious, bi-nerved; rachis c. 0.4 mm wide, 4-angled, flat, brown, narrowly winged, internodes c. 0.6 mm; glumes c. 1.5 mm, cymbiform, keeled, mucronate, sides nerveless, yellow-brown, shiny, margins scarious. Stamens 2; stigmas 3. Nut c. 1.2 x 0.6 mm, rather sharply trigonous, ellipsoid, brown or dark brown, finely papillose.

台灣特有種

Distribution: Weed in Old World tropics and subtropics; most common in SE Asia from India to Japan and Malaysia, west to Tadjikistan, Kazakhstan and Uzbekistan (Aral Sea region), Caucasus, Iraq; E., S. and W. Africa, Madagascar; Australia and Pacific Islands; the Americas.

Tropical, subtropical and temperate regions of both hemispheres.

introduced; Ala., Ark., Calif., Conn., Fla., Ga., Ill., La., Md., Miss., Mo., N.Y., N.C., Okla., S.C., Tenn., Tex., Va., W.Va.; Mexico; Central America; South America; Asia; Africa; Australia.

200-1800 m

Fl. Per.: May - October.

Fruiting summer–fall (Jul–Oct).

In fields, especially rice fields, borders of irrigation ditches; common according to R.R.Stewart (l.c. 1972).

Damp to moderately dry, disturbed soils; 0–500m.

Chlorocyperus iria (L.) Rikli, Jahrb. Wiss. Bot. 27: 564. 1895; Holm & al., World's worst weeds: fig. 95. 1977; K.M. Matthew, Fl. Tamilnadu Carnatic 4: pl.640. 1988.

Cyperus iria (also known as rice flat sedge and rice flatsedge) is a smooth, tufted sedge found worldwide. The roots are yellowish-red and fibrous. The plant often grows in rice paddies, where it is considered to be a weed.