Up to c. 40 cm, lower internodes 2-10 cm by (0.6-)0.75-l.2(-l.7) mm. Leaves (1¼-)2½-4.5(-6) cm by (0.3-)0.8-1.2(-1.6) mm, flat tosubterete or triangular in section, apex acute to obtuse (blade c. 3 mm below the tip 0.2-0.4(-0.5) mm wide); margin on either side with (1-)5-30(-40) conspicuous spiny teeth, sometimes up to the lower 15 mm of the blade unarmed; dorsal surface sometimes with 1-10(-30) spines; spine-cells 0.1-0.25 mm, all (dark) brown; teeth up to as long as half (in the upper part of the blade as long as) the width of the blade; midrib 0.12-0.1 times as wide as the blade; cavities occupying half or almost the entire width of the blade, often with distinct septa. Sheath (2-)2.5-4(-5) by (1.5-)2-4(-6)mm, on either side with (2-)5-12(-20) spines, but unarmed on the inner edge of the auricles; auricles absent to (long-, especially in Indian specimens) triangular, truncate to rounded or almost acute, rarely falcate, (0.1-)0.3-0.6(-1) by (0.3-)0.5-l (-1.5) mm, mostly entire, sometimes toothed or lobed, seldom lacerate up to halfway. Flowers mostly solitary. Male flowers: spathe 2.2-3.6 mm, neck mostly cylindrical, 0.3-1 mm, tip almost truncate to very oblique, entire to up to halfway lacerate; anther subsessile, 4-celled, about elliptical to oblong, (1.2-)1.5-2.2(-2.5) by 0.7-1.2 mm; 'perianth' lobes mostly distinct, (±) nipple-shaped. 'Pedicel' c. 0.2 mm, in anthesis 2.7-3.5 mm. Female flowers: spathe absent (except in some Indian specimens), (1.7-)2-3(-3.4) mm; ovary (0.6-)0.7-0.9(-1.2) by (0.25-)0.3-0.4(-0.45) mm, style (0.4-)0.5-0.8(-1.2) mm, with 2(-1) stigmas (0.4-)0.8-1.6(-1.8) mm. Seeds (1.5-)1.7-2.3 by 0.75-0.9 mm; testa with (14-)16-20(-25) length-rows of (17-)22-25(-30) subquadrate or 5-6-angular areoles, which are mostly slightly wider than long.
Found in a great variety of habitats, in various biotopes of freshwater, mostly shallow but up to 5 m depth, and c. 1000 m altitude, also found in brackish water of fish-ponds near Djakarta with a salinity of up to 30°/00 ( SUNIER Treubia 2 1922 190-195 ), both in everwet regions and in those subject to a dry season. One of the commonest species in Malaysia.
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