Washington State Department of Ecology > Water & shorelines > Freshwater studies > Lake water quality > Aquatic Plant Guide home > Submersed Plants > Ceratophyllym demersum

Aquatic Plant Identification Manual for Washington's Freshwater Plants

Submersed Plants

Species: Ceratophyllym demersum L., coontail, hornwort
Family: Ceratophyllaceae

This underwater rootless perennial plant has branched stems with stiff whorls of forked olive-green to almost black leaves. The leaves are sometimes coated with lime, giving them a crunchy feel. Coontail refers to the thick and bushy growth of leaves (similar in appearance to a raccoon's tail) that occurs at the stem tips. In nutrient rich water, coontail tends to form dense colonies either anchored in the mud or floating freely near the surface.
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Leaf: The 1.5-4 cm long leaves are forked into 2 (sometimes 4) flattened or linear segments with small teeth along one margin. The leaves are often somewhat stiff or crunchy. They are arranged in whorls of 5 to 12 leaves with the whorls becoming dense towards the stem tip.

Stem: The easily broken, freely branching stem is up to 3-4 m long.

Flower: Tiny, submersed flowers are located at the leaf bases. The petals are tiny green scales. Male and female flowers occur separately on the same plant. The male flowers occur in pairs on opposite sides of the stem while the female flowers are solitary. Flowering occurs from June through September.

Fruit: The small (4-7 mm), hard, one-seeded, egg shaped fruit has 3 long spines (to 12mm); 1 spine at the fruit tip and 2 at the base.

Root: Lacks roots. Floats freely below the surface, or is sometimes anchored to the bottom by modified leaves, especially in flowing water.

Propagation: Seed, plant fragments. 

Importance of plant: An important habitat plant for young fish, small aquatic animals, and aquatic insects. Some waterfowl eat the seeds and foliage, although coontail is not considered an important food source. Often used in cool water aquaria and pools.

Distribution: Common worldwide. 

Habitat: Inland and coastal ponds, lakes, and slow moving streams and rivers. Tolerant of hard water (high calcium content) and low light levels.

May be confused with: Less common, non-weedy Ceratophyllum echinatum, which is more delicate, bright green, usually grows in deeper water, and has 3-5 lateral spines on the fruit. Also similar to other bushy submersed plants such as: Muskgrasses (Chara spp.) which are large algae and produce a skunk or garlic-like odor when crushed; waterweeds (Elodea spp.) which have whorls of broad flat leaves; and milfoils (Myriophyllum spp.) which have feather-like leaves.

Photographs: Ceratophyllum demersum plants, closeup of plant

Line Drawings: Ceratophyllum demersum

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