American waterweed
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American waterweed (Elodea canadensis), also known as Common or Canadian Waterweed and Anacharis, is a small, perennial water weed, or submergent macrophyte, native to North America. It is frequently used as an aquarium plant.
American waterweed is usually fairly easy to distinguish from its more notorious relatives, like Brazilian elodea (Egeria densa) and Hydrilla verticillata. All of them have leaves in whorls around the stem. However, American waterweed has three leaves per whorl, whereas the Hydrilla and the Brazilian Elodea almost always have more than three leaves per whorl. Egeria densa is also a much larger, bushy plant with longer leaves. American waterweed also looks very much like another Elodea, Elodea nuttallii, which generally has three narrower leaves per whorl.
The bright green leaves of are born in whorls about the stems, having three or occasionally four leaves per whorl. It lives entirely underwater, the only exception being the small white or pale purple flowers which bloom at the surface and are attached to the plant by delicate stalks. Male and female borne on different plants. The fruit is an ovoid capsule, about 1/4" long containing several seeds that ripen underwater. Seeds are fusiform, glabrous (round), and narrowly cylindrical.
American waterweed grows rapidly in favourable conditions and can choke shallow canals, ponds and the margins of some slow-flowing rivers. It was introduced into Co. Down, Ireland, about 1836, and appeared in England in 1841, spreading through the country in ponds, ditches and streams, which were often choked with its rank growth. It has also been introduced to continental Europe, Asia, and Australia.
Other common names for this plant include Water thyme, Common elodea, Canadian pondweed, and Ditch moss.
References
- [American Waterweed]
- [Canadian Waterweed], by Earl J. S. Rook
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