European Frog-bit

Hydrocharis morsus-ranae

banner image of a mat of European frog-bit
 Image credit: Sigrid Resh

Characteristics 

A member of the Hydrocharitaceae family, European frog-bit (EFB) was Initially introduced in the 1930s as an escapee from an Ontario arboretum. Populations can now be found throughout the Great Lakes watershed ranging from Lakes Ontario to Michigan. Notable infestations are found in the St. Mary’s River on the eastern side of the Upper Peninsula and in northern Wisconsin’s Oconto County. 


This free floating aquatic perennial can be found in shallow, slow moving water near the edges of lakes, streams, ditches and marshes. 

  • Leaves resemble that of native water lilies but much smaller (1-2 in)
  • Leaf surfaces are green in color and may exhibit a purple/red hue on their underside
  • Stems consist of cord-like stolons
  • Roots are often found in entangled clumps, unattached to the substrate
  • Flowers may be present June - August and display three white petals and a yellow center
  • Similar in size to a tic-tac, vegetative buds, or turions, can be found attached to the stolons

As mentioned, EFB can resemble that of native water lilies. This is especially true when the lilies have not fully developed, demonstrating a smaller leaf size similar to that of frog-bit. If it is difficult to identify based on the leaves alone and no flower is present, look to the root system. Native water lilies are attached to a branched rhizome system embedded in the substrate, whereas EFB is not rhizomatous and only rarely anchors itself in shallow waters. For more information, visit U.S. Geological Survey

 

KISMA Management Practices

EFB can form dense, entangled, floating mats which can cover the water surface, thus clogging navigation and irrigation channels and disrupting a variety of recreational activities ranging from water skiing to fishing. Furthermore, infestations have the potential to reduce light, dissolved oxygen, and nutrient availability, negatively impacting native aquatic vegetation and the fauna which depend on it. While we do not have any confirmed EFB sightings in the Keweenaw yet, we’d like to keep it that way. See the following steps and Michigan’s Status and Strategy for EFB Management.

  1. Monitor local waterways and inspect your boat, tackle, and trailer for potential hitchhikers
  2. Clean, drain, and dry all watercraft and equipment when moving to and from launch sites
  3. Report any sightings to your local invasive species management group
  4. If a small infestation is found, hand pulling, raking, and bagging can be effective. It is best to do this early season before the plant produces its turions
  5. Chemical treatment seems advisable for large infestations, however EFB specific herbicide application has yet to be  evaluated for many treatment options. Visit Environment, Great Lakes, and Energy and Michigan’s Status and Strategy for EFB more information regarding permits and chemical treatment.

Note: It is unlikely and unrealistic for the average person to perform widespread chemical or physical management of European frog-bit. It is best to consistently monitor your local area for new signs of invasion in order to address the problem before the plant becomes fully established. If you do happen to come across such a site, reach out to your local invasive species management group who will have the proper resources and connections to handle the invasion.

 

Native Alternatives

If you do happen to remove EFB on your property, it would be a good idea to plant native species in its absence. Floating large-leaved species like white (N. odorata) and yellow water lilies (Nuphar lutea) are great choices as they thrive in similar habitats and may crowd out the invader. Other species such as watershield (Brasenia schreberi) and native pondweeds (Potamogeton spp.) would also be advisable.

 

 

European frog-bit leaf with associated flower and turion bud
(image credit: Sigrid Resh) European frog-bit flower, leaf, and turion
European frog-bit displaying a flower
(image credit: Sigrid Resh) Individual European frog-bit plant. Notice the tangled clump of roots and stolons
underside of European frog-bit leaf

(image credit: Sigrid Resh) the underside of European frog-bit leaves can range in color from reddish purple to olive green 

dumping a bag of hand pulled European frog-bit

(image credit: Sigrid Resh) KISMA crew member dumping a bag of recently removed European frog-bit

Sources

European frog-bit (Hydrocharis morsus-ranae). MISIN, 2020

Hydrocharis morsus-ranae L. USGS, 2021

State of Michigan’s Status and Strategy for European Frog-bit (Hydrocharis morsus-ranae L.) Management. State of Michigan, 2018