Low-growing perennial, very variable, densely tufted, 5-15- (25) cm high, or with prostrate rooting stems with leafy tufts at nodes, often mat-forming, usually reddish-tinged, or submersed. Stems slender, ± swollen at nodes, rooting. Leaves setaceous, short, (very narrow and grass-like in some floating plants), transverse and longitudinal septa present but scarcely visible externally. Inflorescence very variable, unbranched, and few-flowered, or branched and open, with flowers only, or tufts of setaceous leaves with or without flowers. Flowers 2-6 in each cluster. Tepals c.2 mm long, acute, green to brown. Stamens 3-6. Capsule 2-3 mm long, ± = or > tepals, yellowish-brown, oblong to obovate, obtuse, subacute or ± retuse.