European water chestnut is an aquatic plant that is usually rooted in the mud; it bears a rosette of floating leaves at the tip of the submersed stem. Although it grows best in shallow, nutrient-rich lakes and rivers, it can also grow on wet, mucky substrates. It is native to southern Europe and Asia. (Note that this is not the same species used in Asian cooking).
This fast-growing, floating perennial herb forms large mats that shade out native aquatic vegetation. It reduces oxygen levels for fish and encourages sedimentation by restricting silt movement. Hard, pointy seeds can penetrate shoe leather if stepped upon.
Habitat: full sun, grows in water that is several inches to 6 feet deep, prefers water high in nutrients with a neutral or alkaline pH.
Leaves: leaves floating on the surface form a rosette and are waxy, triangular and toothed. Petioles of the rosette leaves have a bladder-like swelling filled with air and spongy tissue.
The conspicuously toothed leaf blades are ½-1 inch long and rhombic in outline (with four sides); the spongy, inflated leaf stalks are up to 3 inches long and provide the buoyancy to keep the terminal leafy portion of the plant floating at the water surface.
Green, feather-like, submersed leaves on the underwater portion of the stem are featherlike and paired (and considered by some to be modified roots).
Flowers: The inconspicuous flowers with their four white petals, each about 1/3 inch long, are borne singly on erect stalks located in the central area of the leafy rosette. Blooms mid to late July and continues until frost.
Fruit: the fruit is a black, four-horned, nut-like structure, about an inch wide, that develops under water. Mature one month after flower forms. Each seed can produce 10 – 15 rosettes; in turn, each rosette can produce 15 – 20 seeds. Easily dispersed in water and can remain viable in sediment for 12 years.
Stem: stems are elongate, flexuous and typically about a meter long but may reach as much as 5 meters in length.
Reproduction: by seed production and fragmentation. Dispersal occurs when rosettes detach and float to new areas. Nutlets and seeds are spread by water currents and waterfowl.
Roots – numerous finely branched roots develop along the lower stem and assist in anchoring the plant to the substrate.
Can be removed mechanically, by hand, or with 2,4-D, which is the only licensed chemical known to control this species.
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