Southeastern Wisconsin Invasive Species Consortium, Inc.


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European Frogbit

European Frogbit

European Frogbit
Genus: Hydrocharis
Species: morsus-ranae


European frog-bit is a free-floating aquatic plant that resembles a miniature water lily. Leaves are thick, heart-shaped, 1 to 2 inches wide and smooth-edged with spongy, purplish-red undersides. Small, showy flowers are ½ inch across, appear singly and have three white petals and yellow centers. Roots are 3 to 8 inches long and unbranched, dangling from the underside of each rosette of leaves. Plants form a thick mat with tangled roots and runners.


European frog-bit can be mistaken for water lily but its leaves are distinctly heart-shaped, leathery and much smaller than any of Wisconsin's water lilies. Water lily flowers are much larger, with more than 3 petals.


European frog-bit is present in New York, Vermont, Michigan and Ontario but is not yet known in Wisconsin. There are two primary methods of reproduction. Plants send out horizontal stems (stolons) which produce daughter plants that can break free and float to new locations. It also produces turions - compact winter buds that sink to the bottom in fall and float back up in spring to grow into new plants. Thick mats of frog-bit inhibit light penetration and can hinder the movement of fish, waterfowl and boats. It prefers quiet waters and can blanket shallow ponds, marshes and the edges of lakes. Like other aquatics, it can spread to new locations from plant fragments attached to boats and trailers.


Plants can be collected by hand or mechanical harvesters, with all parts composted away from aquatic environments. Care must be taken to prevent plant fragments from escaping the infestation site. Sites should be checked annually for reinfestations. Use of chemical herbicides in all Wisconsin aquatic environments (streams, lakes & wetlands) requires a permit from the DNR. Mechanical harvesting may require a permit.