The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Hydrocharis morsus-ranae
Hydrocharis morsus-ranae
(European frogbit)
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Hydrocharis morsus-ranae L.

Common name: European frogbit

Synonyms and Other Names: common frogbit, European frog's-bit

Taxonomy: available through www.itis.govITIS logo

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).

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, 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.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
ME201820181Lower Kennebec
MI1996201915Au Gres-Rifle; Detroit; Huron; Kawkawlin-Pine; Lake Erie; Lake Huron; Lake St. Clair; Lone Lake-Ocqueoc; Lower Grand; Ottawa-Stony; Pigeon-Wiscoggin; Raisin; Saginaw; St. Marys; Thunder Bay
NY1974201821Ausable River; Black; Chaumont-Perch; Grass; Headwaters St. Lawrence River; Indian; Irondequoit-Ninemile; Lake Champlain; Lake Ontario; Lower Genesee; Mettawee River; Middle Delaware-Mongaup-Brodhead; Oak Orchard-Twelvemile; Oneida; Oswegatchie; Rondout; Salmon-Sandy; Seneca; Southern Long Island; St. Regis; Upper Susquehanna
OH200420194Black-Rocky; Cedar-Portage; Huron-Vermilion; Lake Erie
PA201320204Conewango; French; Middle Allegheny-Tionesta; Shenango
VT199320112Lake Champlain; Mettawee River

Table last updated 10/27/2020

† Populations may not be currently present.

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.

Impact of Introduction: The free-floating but stoloniferous growth form can lead to densely tangled floating mats, which can crowd and shade out native aquatic vegetation.  It can dominate wetlands where it occurs, and the dense mats may effect wildlife as well as native plants (Environment Canada 2003).

References: (click for full references)

Aquatic Ecosystem Restoration Foundation (AERF). 2013. Aquatic Herbicides/Agents. Available http://www.aquatics.org/herbicides.html. Accessed 16 April 2013.

Campbell, S., P. Higman, B. Slaughter, and E. Schools. 2010. A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan. Michigan DNRE, Michigan State University Extension, Michigan Natural Features Inventory. 90 pp.

Catling, P.M. and W.G. Dore. 1982. Status and identification of Hydrocharis morus-ranae and Limnobium spongia (Hydrocharitaceae) in northeastern North America. Rhodora 84(840):523-545.

Catling, P. M., G. Mitrow, E. Haber, U. Posluszny, and W. A. Charlton. 2003. The biology of Canadian weeds. 124. Hydrocharis morsus-ranae L. Canadian Journal of Plant Science 83:1001—1016.

Catling, P.M., K.W. Spicer, and L.P. Lefkovitch. 1988. Effects of the introduced floating vascular aquatic, Hydrocharis morsus-ranae (Hydrocharitaceae), on some North American aquatic macrophytes. Naturaliste Canadien 115:131-137.

Cutter, E. G. 1964. Observations of leaf and bud formation in Hydrocharis morsus-ranae. American Journal of Botany 51(3): 318—324.

Daniels, J. 2000. European Frogbit: What is it? Should we be worried? Michigan Sea Grant College Program, Upwellings 22(4).

Environment Canada.  2003.  Factsheet for European Frog-bit (Hydrocharis morsus-ranae).

Falck, M. and S. Garske. 2003. Invasive Non-native Plant Management During 2002. Great Lakes Indian Fish & Wildlife Commission (GLIFWC), Odanah, WI. 68 pp.

Flora of North America.  2008.  efloras.org

Gleason, H. A. and A. Cronquist.  1991.  Manual of Vascular Plants of Northeastern United States and Adjacent Canada.  The New York Botanical Garden, Bronx, NY.

Grant, M. S. 2013. Frogbit. Available http://www.miseagrant.umich.edu/explore/native-and-invasive-species/species/plants/frogbit/. Accessed 16 April 2013.

Great Lakes Panel of Aquatic Nusiance Species (GLPANS). 2008. Prohibitied Species in the Great Lakes Region. 14 pp.

Haynes, R. R. 1988. Reproductive biology of selected aquatic plants. Annals of Missouri Botanical Garden 75(3): 805—810.

Illinois Department of Natural Resources (IL DNR). 2009. Aquatic Invasive Species: European Frog-bit. Available http://www.in.gov/dnr/files/EUROPEAN_FROG-BIT.pdf. Accessed 16 April 2013.

Invasive Plants of Canada Database. 1995. USA records of Hydrocharis morsus-ranae in the Collections of Agriculture and AgriFoods Canada, Central Experimental Farm, Ottawa, Ontario (DAO). Compiled by Erich Haber, Ph.D., National Botanical Services, Ottawa.

Lui, K., M. Butler, M. Allen, E. Snyder, J. da Silva, B. Brownson, and A. Ecclestone. 2010. Field Guide to Aqautic Invasive Species: Identification, collection and reporting of aquatic invasive in Ontario waters. Minstry of Natural Resources, Ontario, Canada. 201 pp.

Mikulyuk, A. and M. Nault. 2011. Hydrocharis morsus-ranae. Available http://www.cabi.org/isc/default.aspx?site=144&page=481&LoadModule=DataSheet&dsID=28140&CompID=5. Accessed 16 April 2013.

Minnesota Department of Natural Resources (MN DNR). 2013. Minnesota invasive species laws. Available http://www.dnr.state.mn.us/invasives/laws.html. Accessed 16 April 2013.

Mudrzynski, B., D.A. Wilcox, and A. Heminway. 2011. Habitats Invaded by European Frogbit (Hydrocharis morsus-ranae) in Lake Ontario Coastal Wetlands. The College at Brockport, State University of New York. 28 pp.

New York Invasive Species Council. 2010. Final report: a regulatory system for non-native species. Department of Environmental Conservation, Albany, NY. 131 pp.

O'Neill Jr., C. R. 2007. European Frog-Bit (Hydrocharis morsus-ranae)- Floating Invader of Great Lakes Basin Waters. New York Sea Grant. 4 pp.

Ontario Invasive Plants Council (OIPC). 2012. #21 European Frogbit. Available  www.ontarioinvasiveplants.ca. Accessed 16 April 2013.

Reznicek A.A., E. G. Voss, & B. S. Walters. 2011. MICHIGAN FLORA ONLINE. University of Michigan.
Available http://www.michiganflora.net/species.aspx?id=1449. Accessed 16 April 2013.

Sager, L. and C. Clerc.  2006.  Factors influencing the distribution of Hydrocharis morsus-ranae L. and Rumex hydrolapathum Huds. in a mowed low-lying marshland, Reserve de Cheyres, lac de Neuchatel, Switzerland.  Hydrobiologia 570: 223-229.

Sarneel, J. M. 2012. The dispersal capacity of vegetative propagules of riparian fen species. Hydrobiologia (online) 7 pp.

Scribailo, R. W. and U. Posluzny.  1985.  Floral development of Hydrocharis morsus-ranae (Hydrocharitaceae).  American Journal of Botany 72(10): 1578-1589.

Thomas, J. D. and P. W. G. Daldorph. 1991. Evaluation of bioengineering approaches aimed at controlling pulmonate snails: The effects of light attenuation and mechanical removal of macrophytes. Journal of Applied Ecology 28(2): 532—546.

Trebitz, A. S. and D. L. Taylor. 2007. Exotic and invasive aquatic plants in Great Lakes coastal wetlands: distribution and relation to watershed land use and plant richness and cover. Journal of Great Lakes Research 33(4): 705—721.

U. S. Environmental Protection Agency (U.S. EPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. Washington DC. 138 pp.

University of Minnesota; Wisconsin Sea Grant Institute. 2003. European Frogbit. Available http://www.seagrant.umn.edu/exotics/frogbit_card.pdf. Accessed 16 April 2013.

University of Minnesota; Wisconsin Sea Grant Institute.  2012. European Frog-Bit (Hydrocharis morsus-ranae). Available http://www.seagrant.wisc.edu/Home/Topics/InvasiveSpecies/Details.aspx?PostID=649
Accessed 16 April 2013.

Villanueva, V. R., L.K. Simolat, and M. Mardon. 1985. Polyamines in turions and young plants of Hydrocharis morsus-ranae and Utricularia intermedia. Phytochemistry 24(1): 171—172

Wisconsin Department of Natural Resrouces (WI DNR). 2012. European frog-bit (Hydrocharis morsus-ranae). Available http://dnr.wi.gov/topic/Invasives/fact/EuropeanFrogbit.html. Accessed 17 April 2013.


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

Revision Date: 8/19/2019

Citation Information:
Jacono, C.C., and L. Berent, 2020, Hydrocharis morsus-ranae L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=1110, Revision Date: 8/19/2019, Access Date: 10/29/2020

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.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2020]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [10/29/2020].

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