Ceratophyllum echinatum A.Gray

Stems to 1 m; apical leaf whorls not densely crowded. Leaves dark green or olive-green, fine-textured. Leaf blade simple or forked into 2-10 ultimate segments (forking of largest leaves 3d or 4th order), proximal segments often conspicuously inflated, mature leaf whorls 25-55 mm diam., marginal denticles weak and inconspicuous, weakly exserted, not raised on broad base of green tissue; 1st leaves of plumule forked. Achene dark green or brown, body (excluding spines) 4.5-6 × 2.5-4.5 × 1.5-3 mm, basal spines 2 (rarely absent), straight or curved, 1-5 mm, marginal spines 2-13, 0.5-6.5 mm, terminal spine straight, 1.5-7.5 mm, margins winged. 2 n = 24.