Perennials, usually submersed aquatic, (10–) 20–100 cm long or tall, without rhizome, with fasciculate roots sometimes having tubercles. Stems floating or creeping and rooting at nodes, branched. Submerged leaves long, narrow, filiform, often overwintering; emergent leaves 10–24 cm long, 2–6 mm in diam., unitubular, visibly perfectly septate and nodose; sheaths lax; auricles large, obtuse, 1–3.5 mm long, to 2.5 mm wide, ±membranous. Lower bract leaf-like, usually shorter (less often equalling or longer) than inflorescence. Inflorescence anthelate, 2.5–10 cm long, lax, of (2–) 4–15 (–20) heads each with 2–6 flowers; pedicels c. 1.0–1.5 mm long; peduncles often flexuous. Tepals 3.5–6 mm long, equal or the inner slightly longer than the outer, lanceolate-ovate, obtuse to subobtuse, castaneous-coloured or brown-reddish, with broad scarious (later inrolled) margins. Stamens 6, more than 1/2 as long as tepals; anthers 1.5–2.5 mm long, 2–4 times as long as the filaments c. 0.6–0.7 mm long; style 0.5–0.8 (–1.3) mm long; stigmas 1.5–2.0 (–3.0) mm long, reddish. Capsule 5–7 mm long, exceeding perianth, trigono-ovoid, subacute, with a 1–1.5 mm rostrum, unilocular, paler castaneous-coloured or brown-reddish, shiny. Seeds ±ovoid, 0.5–0.6 (–0.7) × 0.3–0.4 mm, striate, reticulate.