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Slender, annual herb, 0.02-0.15 m high; amphibious or aquatic, forming tufts; stems erect from creeping stolons, few-branched. Leaves opposite, ± sessile, glabrous, linear, 3-13 x 0.5-1.0 mm, base tapering, apex acute. Flowers axillary, solitary, sessile, monomorphic. Calyx 4-lobed, 0.6-1.0 mm long. Petals absent. Stamens 2; filaments ± 0.1 mm long. Ovary sessile. Style up to 0.25 mm long. Capsule septicidally 2-valved, ellipsoid, exserted from sepals. Seeds small, concave-convex, with evaginating, mucilaginous hairs.
Amphibious, tufted or turf-forming, annual herb. Leaves decussate or rarely in whorls of 3, sessile; blade linear to narrowly ovate, up to 8 mm long. Flowers: minute, subsessile, solitary in axils of bracts; sepal with tube cup-shaped; petals 0; stamens 2; Apr.-Jun. Fruit bright red, ellipsoidal, ± twice as long as calyx tube.
Amphibious, tufted or turf-forming annual herb. Leaves decussate or rarely in whorls of 3. Flowers minute, solitary in axils of bracts. Petals absent. Stamens 2. Capsule opening by 2 valves, ellipsoidal, twice as long as calyx tube.
Leaves 5–15 × 0·5–1 mm., decussate, all narrowly oblong or the upper ones linear-lanceolate, attenuate to the apex, 1-nerved.
Flowers 4-merous, axillary, solitary, sessile or subsessile; bracteoles 0·3–0·5 mm. long, subulate.
Annual caespitose herb up to 5 cm. long when growing on the ground, longer when submerged.
Calyx 0·8–1 mm. long, campanulate; lobes 0·2–0·3 mm. long, triangular.
Stamens 2, included, inserted at the base of the calyx-tube.
Ovary 0·4–0·5 mm. long, ellipsoid; style 0·1–0·2 mm. long.
Capsule c. 1·25 mm. long, ellipsoid, 2-valved, exserted.
Seeds c. 0·5 mm. long, light brown, concave-convex.
Stem unbranched, reddish.
Petals 0.
