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Canadian Waterweed

Invasive Species Information

Canadian Waterweed - Elodea canadensis Biodiversity High Risk Invasive Species 20

What Is Canadian Waterweed - (Elodea canadensis)?

Habitat: Aquatic, freshwater
Distribution in Ireland:

Status: Established

Family name: Hydrocharitaceae

Common name/s: Canadian pond weed

Reproduction: Canadian waterweed is dioecious, with male and female flowers on different plants. Flowers from May to October.

Canadian Waterweed - Elodea canadensis Biodiversity High Risk Invasive Species 20

Canadian Waterweed leaves

Bohemian knotweed - Fallopia x bohemica Biodiversity High Risk Invasive Species 20

Canadian Waterweed leaf

Young plants initially start with a seedling stem with roots growing in mud at the bottom of the water; further roots are produced at intervals along the stem, which may hang free in the water or anchor into the bottom.

 

It grows indefinitely at the stem tips, and single specimens may reach lengths of 3 m or more.

It lives entirely underwater, the only exception being the small white or pale purple flowers which float at the surface and are attached to the plant by delicate stalks.

Canadian waterweed is closely related to Elodea nuttallii, which generally has narrower leaves under 2 mm broad. It is usually fairly easy to distinguish from its relatives, like the Brazilian Egeria densa and Hydrilla verticillata.

 

These all have leaves in whorls around the stem; however, Elodea usually has three leaves per whorl, whereas Egeria and Hydrilla usually have four or more leaves per whorl. Egeria densa is also a larger, bushier plant with longer leaves.

How To Identify Canadian Waterweed?

Bohemian knotweed - Fallopia x bohemica Biodiversity High Risk Invasive Species 20

Canadian Waterweed - Elodea canadensis ID Guide

Leaf: bright green, translucent, oblong, 6–17 mm long and 1–4 mm broad, in whorls of three (rarely two or four) round the stem. 
Flower: three small pinkish/white petals; male flowers have 4.5–5 mm petals and nine stamens, female flowers have 2–3 mm petals and three fused carpels 
Stem: Fleahy, light green/transucent with relish brown nodes at leaf join

Seed: seeds are 4–5 mm long, fusiform, round, and narrowly cylindrical

Fruit: Fruit is an ovoid capsule, about 6 mm long containing several seeds that ripen underwater.

Canadian Waterweed flower

Canadian Waterweed

Bohemian knotweed - Fallopia x bohemica Biodiversity High Risk Invasive Species 20
Bohemian knotweed - Fallopia x bohemica Biodiversity High Risk Invasive Species 20

Why Is Canadian Waterweed A Problem?

Canadian Waterweed is an alien (non-native) invasive plant, meaning it out-competes crowds-out and displaces beneficial native plants that have been naturally growing in Ireland for centuries.

Grows rapidly in favorable conditions and can choke shallow ponds, canals, and the margins of some slow-flowing rivers.

 

This web page is currently under development - we have an anticipated update for early November 2017. 

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European Communities (Birds and Natural Habitats) Regulations 2011 non-native invasive plant species A-Z (Updated 2017)

There are currently 35 invasive plant species listed in the European Communities (Birds and Natural Habitats) Regulations (annex 2, Part 1)...

 

Click on a species from the following list to find out more regarding non-native species subject to restrictions under Regulations 49 and 50.

Non-Native Plant Species identified as High Risk on Ireland's Biodiversity List...

Environment 

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Freshwater

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Marine

Freshwater

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Freshwater

Terrestrial

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Freshwater

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Freshwater

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Risk score 

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18