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Exotic Species


A Few Newcomers in the Rideau River

Flowering rush, Butomus umbellatus.
Flowering rush, Butomus umbellatus.
Aquatic Plants
Flowering rush
Flowering rush (Butomus umbellatus) is a tall shoreline plant with pink flowers. Native to Europe and Asia, it was first discovered in Canada along the St. Lawrence River in 1897. Flowering rush has since spread throughout northern U.S. and southern Canada.

This exotic species appears to be better adapted to flowing water than most native emergent species because it can grow in deeper and faster-moving water. This species is definitely spreading and is a problem along the length of the Rideau River shoreline because it crowds out native species. [3, 4, 5, 6]

European frogbit
European frogbit (Hydrocharis morsus-ranae) is an exotic floating plant plant that looks like a mini water lily. In 1932 this plant was introduced into a pond in the Arboretum of the Central Experimental Farm in Ottawa. The seeds came from Switzerland. The species grew without incident until 1939, when it was seen growing in nearby sections of the Rideau River.

European frogbit, Hydrocharis morsus-ranae.
European frogbit,
Hydrocharis morsus-ranae.

By 1952 this plant had spread to the Ottawa River. By 1982 it had spread to the Great Lakes. Since its introduction in Ottawa, European frogbit has become one of the dominant plants in many eastern-Ontario wetlands, and has reduced native plant biodiversity.

Fortunately, the species is not common in the Rideau River because it is not well adapted to flowing water. This species is not a problem in the Rideau River. [3, 4, 5, 6]

Eurasian water milfoil (Myriophyllum spicatum) in the Rideau Canal.
Eurasian water milfoil (Myriophyllum spicatum) in the Rideau Canal, near downtown Ottawa.

Eurasian water milfoil
Eurasian water milfoil (Myriophyllum spicatum) is an aquatic plant that was first introduced into Ontario and Quebec from Europe in the 1960s. This plant grows in dense mats, thereby choking the navigational channel and disrupting boat traffic and swimming.

Eurasian water milfoil is spread by aquatic birds and boat traffic (on propellers), which transport fragments of the plants to new areas. Fragments are able to root and grow.

In many eastern Ontario rivers, Eurasian water milfoil has displaced native aquatic plant species. Eurasian water milfoil has been found along the length of the Rideau River. Fortunately, this exotic does not seem to be harming other plants or animals along the Rideau River. [3, 4, 5, 6]

Purple loosestrife, Lythrum salicaria.
The flowers of
purple loosestrife
(Lythrum salicaria)
line the Rideau River.

Purple loosestrife
Purple loosestrife (Lythrum salicaria) is a tall shoreline plant with bright purple flowers. It is native to Europe and Asia and was introduced in ship ballast and in livestock feed and bedding in the early 1800s. Since then, garden centres that sell the plants and seeds as wildflowers have also spread it.

Purple loosestrife reduces native biodiversity because it crowds out native plants. In turn the native plant food source and nesting areas for waterfowl are eliminated. [3, 4, 5, 6]

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 Exotic Species
 Don't Overlook...
A Project of the Canadian Museum of Nature
 Images: Ruben Boles