Terrestrial or semi-aquatic. Stem much branched. Leaves opposite, the upper ones semi-opposite to alternate; immersed leaves opposite, pinnate, 0.5-1.2 by 0.6-1.5 mm in outline, with 2-5 c. 0.1 mm wide, filiform lobes; aerial leaves linear, entire or less often ± pinnate, 3-10 mm long, the entire ones 0.3-1.2 mm wide, with a dark cushion-like thickening above at apex, flat, patent. Flowers solitary in the upper leaf-axils, the upper ♂, the lower ♀. Bracteoles inconspicuous or 0. ♂ Flowers nearly sessile. Sepals 0. Petals 2, linear, flat, entire, acute, erect before anthesis and up to 1 mm long, strongly recurvate after anthesis. Stamen 1; filament up to ½ mm; anther elliptic, 0.2-0.6 by 0.1-0.4 mm, mucronate. Rudiment of ovary 0. ♀ Flowers sessile. Sepals and petals 0. Styles shortly conical, distally set with long hairs. Fruit c. 1 mm long. Mericarps 2, ± oblong, at the base with c. 3 dorsal crests, these with 3-5 thin long spines curved upwards, and laterally with some irregular rows of tubercles, upwards slightly narrowing, smooth or with some tubercles, widening at the top in an asymmetrical crown of c. 8-12 ± patent spines with recurvate tips, which are dorsally distinctly longer than laterally, the longest up to 0.8 mm long.
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Perennial monoecious terrestrial or semi-aquatic mat-forming herb. Stems to 5 cm tall. Leaves opposite, becoming alternate above, linear, entire; lamina 3–3.9 mm long. Bracteoles absent. Flowers sessile, solitary. Male flowers reduced; perianth of 2 linear petals 0.4–0.6 mm long, reflexed and strongly rolled at anthesis; stamen 1. Female flowers 2-merous; sepals and petals absent; ovary 2-locular; styles conical; stigmas fimbriate. Fruit sessile, bright red; mericarps cylindrical, 1 mm long, with 3 basal crests each bearing spines 0.1–0.2 mm long, at apex 5 or 6 curved spreading spines 0.3–0.4 mm long.
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