Ceratophyllum demersum

Common Hornwort

Common Hornwort, Photo copyright 2000 by Earl J.S. Rook
Common Hornwort
Photo © 2000 by Earl J.S. Rook

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  • Ceratophyllum, from the Greek, keras (keras), "horn, antler"; and fullon (phyllon), "leaf; foliage"; hence "horn-like leaf"
  • demersum, from the Latin, demersus, "under water"
  • Common name from the shape of the foliage and the Anglo-Saxon wort, "plant"
  • Other common names include Coontail, Rigid Hornwort (UK), Tornfrøet Hornblad (Dan), Karvalehti (Fin), Cornifle Nageante (Fr), Còrn-lus (Gaelic), Rauhes Hornblatt (Ger), Grof Hoornblad (NL), Hornblad (Nor), Rozkatec Ponorený (Slovak), Hornsärv (Swe)


  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Magnoliopsida, the Dicotyledons
      • Subclass Magnoliidae
        • Order Nymphaeales
          • Family Ceratophyllaceae, the Hornworts
            • Genus Ceratophyllum, the Hornworts
  • Taxonomic Serial Number: 18403
  • Also known as Ceratophyllum apiculatum


  • A brittle, rootless, entirely submerged perennial herb.
  • Leaves bright green, stiff, coarse-textured, sessile, in whorls of 5-12 at each node, once or twice forked, ¼"-1¼" long. Leaf segments flat, linear, and coarsely toothed, spreading to curving upward, more crowded toward the branch tips to give the "coontail" appearance. The coarse, weakly and irregularly toothed leaves retain their shape when removed from the water.
  • Stem long, smooth, and delicate, 0-3 branches per node, varying in length according to the depth of the water, the living portion usually no more than 8"-12" long. Stems suspended or anchored by branches buried in sediment.
  • Roots absent, though often anchored to the bottom by pale, modified leaves of root-like appearance..
  • Flowers minute and inconspicuous, submersed, imperfect; male and female flowers on the same plant; solitary and sessile in the leaf axils, both male and female flowers subtended by an involucre or perianth of 8-15 greenish segments/bracts.
  • Male Flower
    • Sepals absent
    • Petals absent
    • Stamens male flowers containing 10-20 stamens;
  • Female Flower a single unicarpellary pistil.
    • Sepals absent
    • Petals absent
    • Pistils 1
    • Ovary superior (within blossom)
  • Fruit a dark olive achene, oval, 1/6"-1/4" long, with 2 basal spurs up to 1/4" long and a beak 1/8"-1/4" long.
  • Seed single


  • A fully submerged aquatic plant.
  • Distinguished from other submerged aquatics by its stiff, forked leaves in whorls.
  • Length and texture of the stems, degree of toothing on the leaves, and character of the fruit are all variable.
  • The only Hornwort (Ceratophyllum spp.) in the North Country.


  • The most common species of Ceratophyllum in North America
  • Nova Scotia to Alaska, south to Florida, Louisiana, Texas, and California into South America. Also Eurasia.
  • Circumpolar, though less common in more northerly regions beyond 60º North latitude.


  • Quiet water of lakes, ponds, marshes, and streams, where it is common, often abundant.
  • A good pond oxygenator, it usually grows submerged in the water but is sometimes found floating on the surface.All Ceratophyllum species are obligately submerged aquatics and cannot tolerate periods of emergence.
  • Typically neutral or alkaline waters.
  • Adapted to grow at relatively low light intensities and therefore may be expected to tolerate shade better than most submerged aquatic plants.
  • Thin submerged leaves and large surface to weight ratios make it an important habitat species for many aquatic invertebrates.
  • Commonly found in plant communities that include species of the genera Elodea (Waterweeds) and Potamogeton (Pondweeds).





  • By seed (rarely),
    • flowers July to September
    • water-pollinated.
  • Most often vegetatively by fragmentation.


  • By division/fragmentation


  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Useful as oxygenator in garden ponds, and as shelter for small fishes and aquatic invertebrates.



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Last updated on 14 April, 2004