National Invasive Species Awareness Week: European frog-bit

Mary Bohling<bohling@msu.edu>, Michigan Sea Grant, and Bindu Bhakta, Michigan State University Extension - February 28, 2015

Learn more about European frog-bit, an aquatic invasive species in Michigan, and what you can do about it.

National Invasive Species Week 2015 is February 22-28. Invasive species are plants, animals and other organisms that are not traditionally found in a given location (in this case the Great Lakes) and create a negative impact of some kind, whether ecological, economic, social and/or a public health threat.

To help celebrate, each day this week Michigan State University Extension is featuring a different aquatic invasive species that has invaded or has the potential to invade Michigan’s environment. Today’s featured aquatic invasive species is the European frog-bit.

Species Name: European frog-bit (Hydrocharismorsus-ranae)

Description: USGS describes this aquatic invasive species as a “Floating (sometimes emergent) perennial herb producing floating leaves (1.2 – 6 cm x 1.2 – 6.4 cm) on long petioles that arise from a central whorl. Roots rarely anchor plants. Leaves are leathery and cordate with arching veins that mimic the leaf outline.”

Similar species: Water lilies (family nymphaeaceae) and water-shield (braseniaschreberi). Midwest Invasive Species Information Network notes that water lilies tend to be much larger than European frog-bit, while water-shield leaves are oval as opposed to European frog-bit’s kidney or heart shaped leaves.

Origin: European frog-bit is native to Europe, as well as parts of Asia.

How it came to the Great Lakes: Sea Grant New York reports that European frog-bit was intentionally introduced in Ottawa, Canada in 1932 to be used as a commercial ornamental plant, escaping cultivation sometime before 1939 when it was found in the wild in Rideau Canal.

How long it has been here: Sea Grant New York shows that in 1952 European frog-bit was collected at Montreal Island in the Ottawa River, in 1976 a population was found on the Canadian shore of Lake Erie, and by 1982 it could be found along the Canadian shore of Lake Ontario. The first sighting in the United States was in 1974 in northern New York.

Extent of range: USGS shows the species spreading to Michigan, New York, Vermont, and Washington in the United States, as well as Ontario, Canada.

Why it is a problem: As Sea Grant Wisconsin explains, European frog-bit mats can grow thick enough to affect boat traffic via tangling, as well as impairing the movement of big fish and diving ducks by not providing enough space between the plants for the fish and ducks to get through.

How it is spread: Indiana DNR reports that European frog-bit is a popular water garden plant and, should it take over a small artificial pond, the owner may attempt to dispose of the plant in natural waterways. Plants can also spread from existing waterways by becoming attached to boats, trailers, or other equipment. Moving water currents can also potentially move the plant around, as the species often isn’t rooted in the ground.

A cool/unusual fact: European frog-bit are dioecious (male and female organs grow on different plants), but most populations are dominated by one or the other sex and seeds are rarely produced. Instead, European frog-bit mainly reproduces by growing buds that break off and grow into a separate plant.

Management actions/options: Right now, hand removal or other harvesting measures seem to be the most effective. However, removal is usually temporary, with plants becoming re-established from dormant buds that break off the original plants, sink to the bottom and become rooted.

What you can do to help prevent the spread:

Prevention is most effective so practicing the Clean, Drain and Dry method for watercraft prior to moving them between lakes. Video

Report it: MDNR, GLANSIS, USGS NAS, and MISIN all accept reports of suspected new introductions. When reporting, it is best to include the date and location of the sighting (with GPS coordinates if possible), a photo, a physical sample and your contact information.

Learn more about how you can help by visiting the Michigan Sea Grant website.

Invasive Species Resources:

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).