Stems to 3 m; apical leaf whorls densely crowded. Leaves bright green, coarse-textured. Leaf blade simple or forked into 2-4(-5) ultimate segments (forking of largest leaves 1st or 2d order, rarely 3d order), segments not inflated, mature leaf whorls 1.5-6 cm diam., marginal denticles conspicuous, usually strongly raised on broad base of green tissue; 1st leaves of plumule simple. Achene dark green or reddish brown, body (excluding spines) 3.5-6 × 2-4 × 1-2.5 mm, basal spines or tubercles 2 (rarely absent), straight or curved, 0.1-12 mm, spine bases occasionally inconspicuously webbed, marginal spines absent, terminal spine straight, 0.5-14 mm, margins wingless. 2 n = 24, 38, 40, 48.
Specimens of Ceratophyllum demersum with short basal spines or tubercles have been misidentified as C . submersum Linnaeus, a species not known in the New World despite reports to the contrary. Ceratophyllum demersum is the most common species of Ceratophyllum in North America and also the least likely to be found with fruit, its reproduction being primarily asexual. Predominantly low leaf order is, therefore, the most reliable means of identifying this species.
Noted for its prolific growth, Ceratophyllum demersum occasionally has attained status as a serious weed.
Plant: perennial, free-floating, submerged herb, rootless; monoecious; STEM flexuous or brittle with irregular branching; tips often with shortened internodes causing dense apical clustering of leaf whorls, these 15-60 mm in diameter when mature Leaves: deep green, simple, or dichotomously divided, forked once, twice, or rarely three times, into 2-4(-6) ultimate segments, that are not inflated; denticles strongly exserted, coarse-textured INFLORESCENCE: sessile or subsessile solitary flowers at nodes, subtended by a whorl of connate foliaceous bracts Flowers: hypognous, greatly reduced; pedicels less than 1 mm long; perianth absent; STAMINATE FLOWERS with 3-many subsessile stamens; PISTILLATE FLOWERS 1-carpelled; style terminal, persistent, elongate-spinescent or short subulate, the apex acute Fruit: moderately compressed achene, the body 3.5-6.0 mm long, 2.0-4.0 mm wide, 1.0-2.5 mm thick, dark green or reddish-brown at maturity, the surface smooth to tuberculate, the faces spineless; terminal stylar spine straight, 0.5-14.0 mm long, persistent; basal spines 2, straight or curved, 0.5-12 mm long, their bases occasionally inconspicuously webbed Misc: Ponds, lakes, slow-moving streams, and river backwaters; 50-2750 m (100-9000 ft); fl Apr-Sep (fr Jun-Oct) REFERENCES: Ricketson, Jon. 1995. Ceratophyllaceae. J. Ariz. - Nev. Acad. Sci. 29(1): 17.
Perennial submersed aquatic herb to 3 m tall Stem: branched, free-floating or buried in substrate, lacking roots. Leaves: whorled, stalkless or nearly so, bright green, whorls 1.5 - 6 cm in diameter, forking once or twice into toothed segments, coarse-textured, usually crowded toward the tip. The first seedling leaves are not divided. Flowers: either male or female, found on the same plant (monoecious), borne in leaf axils, with leaf-like bracts fused at the base but lacking sepals and petals. Male flowers have two-chambered anthers, and female flowers have a single ovary tapering to a persistent spine-like style. Fruit: a one-seeded elliptic achene, dark green to reddish brown, smooth to slightly warty with two straight or curved basal spines (0.1 - 12 mm long) and one straight terminal spine (0.5 - 14 mm long).
Similar species: Ceratophyllum echinatum is a similar species but has fine-textured leaves that fork three to four times, are not distinctly toothed, and are not crowded toward the tip. The winged fruit is warty with several spines.
Flowering: July to September
Habitat and ecology: Common in ditches, lakes and streams, preferably in calcareous water. It tolerates habitat degradation quite well.
Occurence in the Chicago region: native
Notes: Ceratophyllum demersum is the most common species of Ceratophyllum in North America. However, it is also the least likely species to produce fruit, and is mostly asexually propagated. Sometimes it is considered a serious weed due to its prolific growth.
Etymology: Ceratophyllum comes from the Greek words keras, meaning horn, and phyllon, meaning leaf, referring to the horned appearance of the leaves. Demersum means submerged.
Author: The Morton Arboretum
FNA 1997, Jepson 2012, Kearney and Peebles 1969
Duration: Perennial Nativity: Native Lifeform: Forb/Herb General: Herbaceous, aquatic, immersed perennials, stems to 3 m long, thread-like, bright green, flexible with the water currents but brittle, internodes clustered near the tips, branches 0-3 per node, plants overwintering on the bottom as detached, dense shoot tips and winter buds, roots absent. Leaves: Whorled, threadlike, bright green, coarse-textured, simple or dissected into 2-5 very narrow, ultimate segments, the forking of the largest leaves 1st or 2d order, rarely 3d order, the segments not inflated, blades 3-11 per node, 0.8-3 cm long, the segments 2-4, with 2 rows of small teeth distally and 1 multicellular, glandular appendage at the tip, mature leaf whorls 1.5-6 cm diameter, marginal dentations conspicuous, usually strongly raised on the broad base of the green tissue, the first leaves simple, apical leaf whorls densely crowded. Flowers: Uncommon, when present; flowers minute, unisexual, perianths absent, staminate flowers round-topped, 2-5 mm high, stamens pink to red, 30-50, spirally arranged, anthers sessile and exserted from the bracts, pistillate flowers of 1 simple, yellow, ovoid pistil, the margins red-tinged or not, 1-2 mm long, styles elongate, to 1 mm long, filiform, ovary superior, inflorescences with 1-3 flowers per cyme but looks to be 1 and subtended by a calyx-like whorl of 8-15 bracts, these linear, leaf-like, and fused at the base, with toothed apices, persistent in fruit, axillary cymes becoming reduced near shoot tips, inflorescences axillary, sessile to subsessile, 1-several per node, staminate below and pistillate above, flowers water pollinated. Fruits: Achenes dark green or reddish brown, the body (excluding the spines) 3.5-6 mm long, 2-4 mm wide and 1-2.5 mm thick, basal spines or tubercles 2 or rarely absent, straight or curved, 0.1-12 mm long, the spine bases occasionally inconspicuously webbed, marg Ecology: Found in fresh to slightly brackish rivers, acidic to alkaline, with medium to high nutrient levels, in water 0.1-4 m deep, in streams, ditches, lakes, ponds, pools, marshes, swamps, and slow watercourses, from 2,000-6,000 ft (610-1829 m); flowering sprin Distribution: Widespread throughout the United States and worldwide. Ethnobotany: Unknown. Synonyms: Many, see Tropicos Editor: LCrumbacher2012 Etymology: Ceratophyllum comes from the Greek keras, "a horn," and phyllon, "leaf," alluding to the stiff and narrow leaf divisions, this is a genus often called hornwort, and demersum means living under water, submerged.
Stems elongate, freely branched, forming large masses; lvs in whorls of 5-12, rather stiff, variable, 1-3 cm, mostly once or twice forked, the ultimate segments linear, flat, 0.5 mm wide, but nearly doubled in width at the broad, antrorse teeth; achene ellipsoid, 4-6 mm, with 2 basal spines; first 2 pairs of plumular lvs unbranched; 2n=24. Abundant in quiet water; widespread from s. Can. to S. Amer., and widely distributed in the Old World.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.