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.
"Much like no. 1 [Ceratophyllum demersum L.]; lvs more flaccid, the larger ones mostly 3(4) times forked, the ultimate segments commonly narrower, entire or with a few small, very slender teeth; achenes with several unequal marginal spines as well as 2 basal ones, conspicuously tuberculate on the surface; all plumular lvs forked. Quiet water; N.S. and N.B. to B.C., s. to Fla. and trop. Amer.; less often collected than no. 1."
|Hornwort, cornifle échinée|