Hydrocharis morsus-ranae L.

Common Name: European frogbit

Synonyms and Other Names:

common frogbit, European frog's-bit

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Identification: Hydrocharis morsus-ranae is a free-floating aquatic plant with leathery, heart-shaped leaves and small white flowers with three petals. The root system is well developed, but does not normally anchor the plant to the substrate. The species spreads by sending out runners, and can form dense, tangled mats (Environment Canada 2003).

The growth form is stoloniferous, the stolons having seasonally dimorphic terminal buds with one root. The leaves are petiolate and floating or, in dense vegetation, emergent.  The leaf blade is ovate to orbicular in shape, typically measuring 1.2-6 x 1.3-6.3 cm, with a chordate to reniform base, and entire margin.  Veination is palmate with cross-veins. The primary veins form a 75--90° angle with the midvein and are broadly curving.  Aerenchyma are confined to the midvein region (not margin to margin as in Limnobium).  Individual aerenchyma space, located approximately 1 mm from either side of midvein, typically measures 0.1-0.5 mm across its longest axis (eFloras 2008; Gleason and Cronquist 1991).

The species is dieocious (male and female flowers found on separate plants). Both sexes of flowers have an outer whorl of three greenish-red sepals, and a whorl of three membranous white petals.  Staminate (male) flowers occur in cymose inflorescences of 2 to 5 flowers on pedicels up to 4 cm long.  The inflorescence is enclosed by a spathe of one or two scale leaves which subtend the first two flowers.  The stamens number 9 to 12 and are arranged in 3 trimerous whorls, with an innermost whorl of staminodes.  The first and third whorls of stamens are partially united along their filaments, and the second whorl of stamens is fused to the staminodes.  The anthers are basifixed and consist of four micro-sporangia, with pollen grains dehiscing through lateral slits.  In the center, there is a large pistil-like structure (Scribailo and Polsluzny 1985).

Pistillate (female) flowers are solitary and enveloped in a tubular hypanthium, with pedicels up to 9 cm long. The ovary is inferior, with six dorsiventral styles.  Each style is bifurcated at the end into two flat, papillose stigmas. There is a whorl of nectaries that occur as appendages on the three antipetalous styles, and a whorl of filament-like staminodes.  he fruit is a berry that dehisces longitudinally, releasing seeds 1 to 1.3 mm in length (Scribailo and Polsluzny 1985).


Native Range: Europe and northern Asia. Threatened in parts of its native range; endangered in Switzerland (Sager and Clerc 2006).

Great Lakes Nonindigenous Occurrences: Hydrocharis morsus-ranae was planted in ponds beside Dow’s Lake in the Central Experimental Farm Arboretum at Ottawa in 1932 (P. M. Catling and W. G. Dore 1982). It apparently escaped from these ponds; by 1939 it was found in the Rideau Canal and by 1967 in the St. Lawrence River from Montreal as far as Lake St. Peter. It has been known from the Canadian shoreline of Lake Erie since 1976, and has also spread into Lake Ontario and localities in New York (Catling and Dore 1982).

European frog-bit was first recorded in the United States in 1974 from the Oswegatchie River, a tributary of the St. Lawrence River, in northern New York. By the early 1980s, occurrence in that state increased to inland sites south of the St. Lawrence River, and by the early 1990s, to bays and marshes along Lake Ontario (Catling and Dore 1982; Invasive Plants of Canada Database 1995). By 2000, it had spread to eastern New York, in the southern reaches of Lake Champlain, at Mill Bay (pers. comm. H. Crosson, Vt. Dept. Env. Cons. 2001).

European frog-bit was first discovered in Lake Champlain during 1993 at its northern reaches, near Grande Isle, Vermont. It appeared confined there until 1999 when plants were first found along the southern shore of Lake Champlain at Benson, Orwell and West Haven, VT (pers. comm. H. Crosson, Vt. Dept. Env. Cons. 2001).

European frog-bit was identified in 2000 as new to the state of Michigan, where populations are known from two sites: 1) Lake St. Clair marshes and 2) Detroit River marshes.  A few unidentified plants were first observed in a dredged slough at Lake St. Clair in 1996. Within two years plants had become abundant throughout the marsh and formed dense mats in cut ponds. The Detroit River marshes lie downstream of Lake St. Clair. Both localities drain the Detroit River which flows into Lake Erie (J. Daniels 2000; pers. comm. J. Champion, Huron Clinton Metroparks, and A.A. Reznicek, Univ. of Mich., 2001).

Canada: Southeastern Ontario and adjacent western Quebec, including the Ottawa, Rideau and St. Lawrence Rivers and the shorelines of Lake Ontario and Lake Erie.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Hydrocharis morsus-ranae are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI1996202219Au Gres-Rifle; Black-Macatawa; Detroit; Huron; Kawkawlin-Pine; Lake Erie; Lake Huron; Lake Michigan; Lake St. Clair; Lone Lake-Ocqueoc; Lower Grand; Ottawa-Stony; Pere Marquette-White; Pigeon-Wiscoggin; Raisin; Saginaw; St. Marys; Thunder Bay; Upper Grand
NY1974202219Ausable River; Black; Chaumont-Perch; Grass; Headwaters St. Lawrence River; Indian; Irondequoit-Ninemile; Lake Champlain; Lake Ontario; Lower Genesee; Mettawee River; Niagara River; Oak Orchard-Twelvemile; Oneida; Oswegatchie; Raquette; Salmon-Sandy; Seneca; St. Regis
OH200420226Ashtabula-Chagrin; Black-Rocky; Cedar-Portage; Huron-Vermilion; Lake Erie; Sandusky
VT199320225Lake Champlain; Mettawee River; Missiquoi River; Otter Creek; Winooski River
WI202120223Lake Michigan; Menominee; Peshtigo

Table last updated 11/28/2023

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: Hydrocharis morsus-ranae is found in slow-moving waters in bays, ponds, open marshes and ditches, and along protected edges of lakes and rivers (Campbell et al. 2010, Lui et al. 2010). It grows well in calcium-rich waters (O'Neill Jr. 2007). The leaves are able to float on the top of the water because of their spongy underside (IL DNR 2009).

Hydrocharis morsus-ranae is a dioecious plant, meaning that the male and female flowers occur on different plants (IL DNR 2009). Populations are typically only contain one sex, therefore sexual reproduction and seed production is quite low (Campbell et al 2010, IL DNR 2009). Instead, common frog-bit expands by produces stolons, which can produce juvenile plants (O’Neill Jr. 2007). In the autumn, the ends of the stolons produce turions (vegetative buds that survive through the winter), which break off the main plant, sink to the bottom of the waterbody, and go dormant (Cutter 1964, O’Neill Jr. 2007). In the spring, the turions float to the surface and begin growing (IL DNR 2009). About half of H. morsus-ranae propagules are still able to float after being in the water 6 months; indicating that dispersal via waterways is probably essential to the expansion of this species (Sarneel 2012). A single H. morsus-ranae plant can create 100-150 turions in a single growing season (IL DNR 2009, O’Neill Jr. 2007).

Means of Introduction: Unintentional release into Lake Superior in 1972 (U.S. EPA 2008).  Plant dispersal (aided by motor boats) through aquatic systems; entering from Canada, where in the 1930s it first escaped ornamental cultivation.

Status: Established where recorded.

Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...


Hydrocharis morsus-ranae has a moderate environmental impact in the Great Lakes.
This species is also capable of aggressive growth: one hibernaculum (starting material for a new plant) can grow to cover an area one diameter in diameter in a single season (Haynes 1988). The free-floating form can lead to densely tangled floating mats, which can crowd and shade out native aquatic vegetation (Catling et al. 2003, Grant 2013). Populations of H. morsus-ranae can also compete for nutrients and gases; further reducing the growth of nearby vegetation (Lui et al. 2010). There was a 95% decline submerged vegetation species below mats of H. morsus-ranae (Catling et al. 1988 in Mudrzynski et al. 2011). There is are discrepancies regarding the extent of H. morsus-ranae in the Great Lakes. Trebitz and Taylor (2007) state that this species rarely becomes dominant in Lakes wetlands. However, there have also been reports that H. morsus-ranae population have been aggressively growing in large areas of shallow, open waters in Michigan (Reznicek et al. 2011). 

As colonies H. morsus-ranae displace native plants; other native aquatic life experience a reduction in food and habitat (Environment Canada 2003, WI DNR 2012). Dense mats can inhibit the movement of waterfowl or larger fish; which could alter predator/prey cycles as the waterfowl and fish move to other locations to find food (O’Neill Jr. 2007, University of Minnesota, Wisconsin Sea Grant Institute 2012).  Catling et al. (1988) surveyed live H. morsus-ranae mats and found a decline in snails, crustacean, and insect larvae (in Mudrzynski et al. 2011).

Dense stands can alter the water flow or currents (Mikulyuk and Nault 2011). In the autumn, H. morsus-ranae dies and sinks to the bottom of the water body, where it decomposes (IL DNR 2009).  Altered hydrology and/or increased decomposition can reduce oxygen concentration in nearby waters and could potentially lead to the death of nearby plants, insects or fish and insects (Catling et al. 2003, IL DNR 2009). However, Thomas and Daldorp (1991) found that the addition of the H. morsus-ranae had no effect on the macrophyte community or on the dissolved oxygen profiles.

Hydrocharis morsus-ranae has a moderate socio-economic impact in the Great Lakes.
Large infestations of H. morsus-ranae have reduced water currents in canals and irrigation systems (Catling et al. 2003). Dense layers of tangled stems and roots can wrap about boat propellers and impede water traffic (Lui et al. 2010, University of Minnesota Wisconsin Sea Grant Institute 2012). Large populations of common frogbit also limit recreational activities such as swimming, fishing, and waterfowl hunting (Grant 2013, Lui et al. 2010, University of Minnesota Wisconsin Sea Grant Institute 2003).

The decreased recreational and aesthetic value linked to large populations of H. morsus-ranae can lead to a reduction in property value along the affected waterfront and even cause declines in tourism and associated revenue (Mikulyuk and Nault 2011).

There is little or no evidence to support that Hydrocharis morsus-ranae has significant beneficial effects impacts in the Great Lakes.
Some species of water birds, fish, and insects feed on H. morsus-ranae (O’Neill Jr. 2007).

Some property owners consider it to have aesthetic appeal and it is used in water gardens (New York Invasive 2012).

Spermidine, an anti-aging compound, can be found in dormant turions of H. morsus-ranae (Villanueva et al. 1985).

Management: Regulations (pertaining to the Great Lakes)

Prohibited in Illinois, Michigan, Minnesota, and Wisconsin (GLPANS 2008). In Minnesota, possession, import, purchase, transport, or introduction of H. morsus-ranae will result in a misdemeanor (MN DNR) 2013).

The New York Invasive Species Council ranks this species as posing a very high ecological threat and recommends that it be regulated (New York Invasive 2010).

The Great Lakes Life & Wildlife Commission have no found H. morsus-ranae in their ceded territories, but recommend immediate control upon detection (Falck and Garske 2003).

Hydrocharis morsus-ranae is restricted in Ontario (regulatory amendments to Ontario Regulation 354/16 under the Invasive Species Act, 2015).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Grass carp, Ctenopharyngodon idella, feeds on H. morsus-ranae. However, this introduction of this species may also have a negative effect on native vegetation, which might outweigh the benefits of H. morsus-ranae control (Mikulyuk and Nault 2011).

Mowing does not control H. morsus-ranae population (Sager and Clerc 2006). Removing manual harvesting may provide temporary control (IL DNR 2009, WI DNR 2012). To improve efficacy of this method, harvesting should occur in the spring; after the turions have begun growing, but before dense mats form (Catling et al. 2003).

Another possible method for small water bodies would be to have a water draw-down after turions have germinated, but before extensive growth occurs (Catling et al. 2003).

Diquat, imazapyr, penoxsulam, and imazamox offer excellent control of H. morsus-ranae (AERF 2013).

Application of flumioxacin by backpack sprayer is proving effective (European Frogbit Collaborative 2021, Personal Communication).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

References (click for full reference list)

Author: Jacono, C.C., and L. Berent

Contributing Agencies:

Revision Date: 11/13/2023

Citation for this information:
Jacono, C.C., and L. Berent, 2023, Hydrocharis morsus-ranae L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=1110&Potential=N&Type=1&HUCNumber=DGreatLakes, Revision Date: 11/13/2023, Access Date: 11/28/2023

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.