Coontail (Ceratophyllum demersum) is a completely submersed plant commonly seen in Washington lakes with moderate to high nutrient levels. It is also known by the common name hornwort. The common names refer to its full, bottle-brush-like growth form and its forked, antler-shaped leaves. The Latin name Ceratophyllum pertains to the horned leaf edges - Cerato derives from the Greek word "keras" (horn, as in rhinoceros). Phyllum means leaf.
The serrated, forked leaves of coontail are arranged on the stems in whorls, with usually 5-12 leaves in each whorl. It is generally a dark, olive green color, and is often rather hard and crusty to the feel. This is especially true where it grows in hard water lakes (the calcium in the water becomes deposited on the leaf surface, making it seem crunchy).
The tiny flowers of coontail are located at the leaf bases. Each flower is either male or female, though both are borne on the same plants. The flowers are on very short stalks, so they never grow to the water's surface. This means pollination must occur under water. Coontail accomplishes this by releasing the stamens from the male flowers. These stamens rise to the surface where they split open and release their pollen. In still water, the pollen grains sink slowly, pollinating any female flowers they come in contact with. The release of pollen in the water is unusual, even for aquatic plants. Because pollen usually needs to be dry until it reaches the female flower, most aquatic plants have flowers which rise above the surface to be pollinated by insects or wind. However, the pollen of coontail has adapted to being wet, so the plant can complete its entire life cycle under water. After pollination, a small, hard, oval seed with 3 spines is produced. Coontail spreads to new areas either through germination of these seeds, or by regrowth of stem fragments.
Coontail does not produce roots, instead it absorbs all the nutrients it requires from the surrounding water. If it is growing near the lake bottom, it will form modified leaves which it uses to anchor to the sediment. However, it can float free in the water column, and sometimes forms dense mats just below the surface. Because it gets nutrients from the water, it grows best where these nutrient levels are high. It will also tolerate a wide range of water hardness, even growing in some highly alkaline lakes of central Washington.
This plant is often used in cool-water aquariums, and because it is a native plant, it makes a good choice for local aquarium hobbyists. It is also used as an oxygen plant for aquatic gardens. In the wild it provides habitat for young fish and other aquatic animals. Waterfowl will eat the seeds and foliage, though it is not a favorite food plant. Coontail is found growing in most parts of the world and can cause weed problems where it has been introduced outside its native range.
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