Robust aquatic annual up to 160 cm high, the basal part often immersed in water and rooting profusely at the nodes. Leaf sheaths glabrous or pilose with bulbous-based hairs; leaf laminas 20–45 cm × 3–12 mm, broadly linear. Racemes 4–10 cm long, slightly dorsiventrally flattened, glabrous, terminating in a tail of reduced spikelets, gathered into a spathate false panicle. Sessile spikelet oblong, pallid; callus elliptic with low central ridge; inferior glume 3–4 mm long; superior glume boat-shaped with a winged keel, this thrust between the internode and pedicel, sometimes conspicuously protruding. Pedicelled spikelet 5–7 mm long, ovate, herbaceous, green; pedicel shorter than the internode, the two fused only in the inferior part.