European frog-bit

  • European frog-bit


    (Hydrocharis morsus-ranae)


    European Frog-bit is an invasive aquatic plant native to Europe and parts of Asia and Africa. Imported from Europe in 1932 for possible commercial use as an ornamental plant, it was first observed in the Rideau Canal in 1939. It has since spread to the St. Lawrence River, Lake Ontario, Lake Erie and several rivers and inland lakes. A rapid growing plant, it prefers calcium-rich water and forms dense floating mats with free-floating roots up to 30 cm long in slow moving water bodies such as marshes, swamps, quiet bays and shorelines, sheltered coves and poorly drained ditches.

    European Frog-bit is an annual plant that reproduces primarily by producing juvenile plants from stem-like extensions during the growing season and new plants from winter buds, called turions, that sink to the water bottom to lie dormant over the winter and float to the surface in spring. The plant can spread between water bodies via seeds, plant fragments and turions spread by boats and equipment. A single plant produces 100 to 150 turions each year.

    Control methods include hand and mechanical harvesting, although care must be taken to prevent fragments from escaping the infestation site. Chemical herbicides are also effective, where permitted by law.




    European Frog-bit is found in southern Ontario and along the St. Lawrence River in Quebec, with isolated populations in New York, Vermont, Michigan and Washington and the southern margin of the Canadian Shield.



  • Identification

    • Although European Frog-bit looks like other native aquatic plants, it differs in the following ways: North American frog-bit (Limnobium spongia) has a spongy coating on the bottom of the leaf; Watershield (Brasenia schreberi) leaves do not form a rosette (cluster); and White Water Lily (Nymphaea odorata) has much larger leaves when mature, from 15 to 30 cm across.
    • The plant floats freely on the water surface due to its free-floating roots which do not root in the water bottom.
    • It has round to heart-shaped smooth leaves about 2.5 to 5 cm wide with purple-red bottoms and a spongy coating along the middle vein. The leaves form a rosette up to 6 cm wide.
    • Produces flowers up to 2 cm wide from spring to fall with three rounded petals and a yellow centre. Berries are spherical with many seeds.


    • A fast growing plant, it can form dense, intertwining mats that reduce biodiversity by crowding out native plants and blocking sunlight from submerged plants.
    • When a colony of plants die and decompose, oxygen is depleted from the water which can affect fish and other aquatic life.
    • Tangled masses of Frog-bit can interfere with swimming and boating and clog drainage canals and streams.

    Help Stop the Spread

    • Learn to identify European Frog-bit and how to prevent spreading this plant with your watercraft.
    • Avoid infested areas or reduce speed when travelling near infestations as waves can dislodge plants and cause them to spread to new areas.
    • Inspect your boat and equipment and remove any plants, animals or mud before leaving a water body.
    • Avoid planting European Frog-bit in your aquarium or water garden; use only native or non-invasive plants.
    • Do not release aquarium plants or pets into any waterbody.
    • If you see European Frog-bit or a plant that you think might be this invader, report it on the toll-free Turtle Island Invaders hotline at 1-844-872-2348 (1-844-TRACE-IT) and report it to your local Lands or Natural Resources officer. Be sure to include understandable directions to the location.
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