Eleocharis tetraquetra Nees

Tufted perennial, 20-50 cm. Rhizome rather short, 1-1.5 mm diam., horizontal. Stem 0.5-1 mm diam., trigonous or tetragonous, edges sharp, sides with 1-3 raised veins, smooth, glossy, greyish green. Open sheaths to c. 10 mm; lower closed sheath c. 25 mm, scarious, pale brown or reddish brown for whole length, mouth oblique; upper to 65 mm, pale brown or lowest part often reddish, mouth straight or slightly oblique; blades 0 or minute notch. Spike 5-15 x 2.5-4 mm, from ellipsoid or ovoid to almost globose, with c. 20 to 50 rather closely imbricating glumes; basal glumes 2, sterile, 2-3.5 mm, almost equal, mid-nerve strong, surrounded by brown zone, margins widely scarious; glumes 3-3.5 x c. 1.5 mm, cymbiform, mid-nerve not reaching rounded apex, sides in apical part brown or reddish brown, margins widely scarious. Perianth bristles 4-7, equalling nut (incl. stylopodium), brown, subplumose, with wide, soft, spreading or reflexed barbs; stamens 3, anthers 1.3-1.5 mm; stigmas 3. Nut 1.5-1.8 x 0.9-1.3 mm (excl. stylopodium), ovoid, obtusely trigonous, plano-convex, brown or greenish brown, finely reticulate, glossy; stylopodium 1.1-1.2 x 0.7-0.8 mm, much longer than wide, conical, trigonous, edges convex, white or yellowish, densely hairy, not clearly constricted from nut.

Distribution: Afghanistan, Pakistan, India, Sri Lanka, China, Japan, south to New Guinea and Australia.

Fl. Per.: August.

Wet meadows with flowing water, up to 2100 m.

Eleocharis tetraquetra là loài thực vật có hoa trong họ Cói. Loài này được Nees mô tả khoa học đầu tiên năm 1834.

四角蔺（学名：Eleocharis tetraquetra），又名龙师草，为莎草科荸荠属下的一个种。