Herbs monoecious, aquatic, sometimes forming dense stands. Stems branched or unbranched, to 3 m. Turions present, becoming brown to red-brown at maturity, clavate to obdeltoid, with abrupt transition from foliage leaves to reduced turion leaves, (6–)11–37(–52) × (3–)4–6(–9) mm, apex ± rounded, lateral turions with several whorls of minute, brown prophylls, entire proximallyand toothed to lobed distally, ovate to elliptic or lanceolate in outline; leaves pectinate, strongly appressed to axis throughout, narrowly flabelliform in outline, 4.5–7.5 × 1.2–1.8(–4) mm; segments 8–12(–18), flattened, linear-lanceolate, longest segment 1.5–6 mm, basal segment usually greater than or equal to 2/3 central axis of leaf, apex ± acute, trichomes usually absent. Leaves in whorls of (3 or)4, heteromorphic; petiole to 6 mm; submersed leaves pectinate, ovate to elliptic in outline, (7–)12–30(–46) × 9–24(–40) mm, segments (9–)12–22(–34), linear-filiform, longest segment (2–)6–19(–29) mm; emersed leaves pectinate, lanceolate to elliptic to ovate in outline, 2–5(–15) ×0.9–2.6 mm, segments (9–)12–20, greater than 0.5 mm. Inflorescences to 25 cm; flowers proximally pistillate, medially bisexual, distally staminate, in whorls of 4; bracteoles cream, ovate, 0.3–0.6(–1) × 0.1–0.6(–1.3) mm, margins deeply dissected into irregular lobes. Staminate flowers: sepals cream, narrowly triangular to deltate, 0.5–0.7(–0.9) × 0.4–0.6(–0.8) mm; petals persistent, cream, sometimes apically suffused with purple, elliptic to obovate, 1.8–2.2(–2.4) ×0.7–1.5 mm; stamens 8, filaments to 2 mm, anthers 0.8–1.7 × 0.3–0.6 mm. Pistillate flowers: sepals greenish to cream, elliptic to triangular, 0.2–0.7 × 0.2–0.7 mm; petals often caducous, sometimes persistent, cream to purple, elliptic to obovate, 0.4–0.7(–0.9) × 0.3–0.5(–0.8) mm; pistils (1.3–)1.8–2.7 mm, stigmas red to± purple, to 0.8 mm. Fruits globose, shallowly 4-lobed. Mericarps olive-green to brown, subglobose to globose, 2–2.7(–3) × (0.9–)1.1–1.3(–1.7) mm, transverselywidely obovate, abaxial surface broadly rounded to moderately flattened, smooth, often with 2 shallow longitudinal ridges, wings and ribs absent. 2n = 28.