European frog-bit: Be on the lookout for this aggressive invasive plant

European frog-bit is a prolific invasive aquatic plant that is creating a mess along the shores of the Great Lakes.

Figure 1: European frog-bit observations in Michigan. The red points indicate a specific location reported to MISIN. Map created by MISIN.

Figure 1: European frog-bit observations in Michigan. The red points indicate a specific location reported to MISIN. Map created by MISIN.

What is European frog-bit and how did it get to Michigan? 

European frog-bit (Hydrocharis morsus-ranae) is a free-floating aquatic plant with multiple miniature lily pad shaped leaves. This prolific invasive species is spreading along the shorelines and wetlands of Lakes Erie, Huron and Ontario. European frog-bit was brought from Europe to the Central Experimental Farm in Ottawa in 1932 as an ornamental plant. By 1939, it had escaped and spread to the Rideau Canal in Ottawa, Canada (Catling and Dore, 1982). Since then it has continued to spread into several rivers, Lake Ontario, Lake Erie, Lake Huron and other inland waters. In Michigan, European frog-bit is now common along the coastline of Lakes Huron, Erie and Lake St. Clair where emergent vegetation like cattail and phragmites protect European frog-bit from waves and currents. Figure 1 displays the current Midwest Invasive Species Information Network (MISIN) European frog-bit locations in Michigan. It is important to note that at this time there are very limited sightings in Michigan’s inland waters and it would be good to stay that way.

Why should we worry about European frog-bit? 

European frog-bit is listed on Michigan’s Aquatic Invasive Plant Watch List, which identifies species that present an immediate and significant threat to Michigan’s natural resources. European frog-bit produces dense, floating mats that cover large areas of shoreline. These mats can hinder recreation, reduce waterfowl and fish habitat, and reduce light conditions for beneficial native aquatic plants. To learn more about the impacts of European frog-bit, see the State of Michigan Invasive Species Alert for European frog-bit

How to identify European frog-bit?

European frog-bit is predominately free-floating, meaning it rarely roots to the bottom of a waterbody. However, in water under two feet deep, European frog-bit can become rooted. The leaves look like miniature lily pads, about the size of a silver dollar.  In contrast, Michigan’s native water lilies have sturdy roots anchored to the waterbody bottom and have much larger leaves.  

To identify European frog-bit, look for:

  • Free-floating or rooted plant with leaves that arise from a single point
  • Leaves are round/heart shaped and resemble little (0.5 – 2.25 inches) water lilies
  • Leaves have a dark purple underside with a spongy area around the midvein of the leaf
  • White flowers with three petals and a yellow center

For more identification tips see the MISIN European frog-bit fact sheet.

What should you do if you identify European frog-bit? 

Report it immediately, especially if found in inland lakes, rivers, streams, ponds or wetlands.  The report can be submitted through MISIN, to the Michigan Department of Environmental Quality – Water Resources Division at 517-284-5593 or by contacting your local Cooperative Invasive Species Management Area (CISMA). It is important that sightings are reported immediately because early detection is the essential first step for successful control.

How can you help combat the European frog-bit invasion? 

First, take precautions to prevent spreading European frog-bit from one water body to another. This means carefully cleaning your equipment, boat and trailer before traveling to another waterbody. If you would like additional information about decontaminating your equipment please visit the Clean Boats Clean Water Program. You can also assist with removal efforts directly. If you live on the east side of the state contact your local CISMA to find out about European frog-bit pull events. 

As new invaders come into Michigan it is critical that they are reported as soon as possible so that eradication can be successful. European frog-bit is spreading rapidly along the coasts of Lake Huron, Lake Erie and Lake Ontario, but there is still hope for our inland waters. Also, we might be able to keep European frog-bit from spreading further in the Great Lakes by controlling it where it is currently found.  It is important that boaters and anglers take time to clean off their equipment, boats and trailers after leaving these infested waters and before entering other waterbodies. Working together, we can keep this plant invader contained and in check.

Reference:

Catling PM and Dore WG. 1982. Status and identification of Hydrocharis morsus-ranae and Limnobium spongia (Hydrocharitaceae) in Northeastern North America. Rhodora, Vol. 84, pp. 523-545.

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