Elodea canadensis

American or Canadian waterweed, Elodea canadensis, is one of the oldest and most well-known aquarium plants, even though it is hardly ever found in aquaria today but is rather used as a pond plant. It became "famous" in Europe due to its extremely high reproduction rate in many waterbodies, after it was introduced from North America in the 19th century. Later on these populations declined sharply, and today, E. canadensis is only rarely found in nature, less frequently than Elodea nuttallii (Nuttall's waterweed), which has also been introduced from North America and is still spreading. Both species are hard to discern, and often E. nuttallii is mistakenly sold under the name "E. canadensis" as pond plant in trade.

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