Hornwort, cornifle échinée

Ceratophyllum demersum Linnaeus var. echinatum (A. Gray) A. Gray; C. submersum Linnaeus var. echinatum (A. Gray) Wilmot-Dear

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.

Flowering spring-summer. Fresh water of lakes, ponds, marshes, swamps; 0-500 m; B.C., Man., N.B., N.S., Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass, Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., R.I., S.C., Tenn., Tex., Vt., Va., Wash., W.Va., Wis.

Principally an eastern North American species--and the only species of its genus endemic to North America-- Ceratophyllum echinatum is disjunct in the Pacific Northwest as a result of repeated Pleistocene glaciation. The habitats of C . echinatum are typically more acidic (avg. pH 6.6) than those of C . demersum (avg. pH 7.4). The two species only rarely coexist. Ceratophyllum echinatum also thrives in cooler, clearer, and more oligotrophic water than C . demersum and often is found in more ephemeral sites, such as shrub swamps (e.g., with Cephalanthus occidentalis ) and beaver ponds.

This species, relatively uncommon, is fast disappearing from much of its range because of habitat alteration or destruction and the introduction of nonindigenous species; steps should be taken to secure its conservation. Unlike Ceratophyllum demersum , C . echinatum does not attain status as a serious weed.