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| NAS - Nonindigenous Aquatic Species |
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Common Name: common frogbit
Synonyms and Other Names: Also known as European frogbit.
Taxonomy: available through 
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. The 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).
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Interactive maps: Continental US, Alaska, Hawaii, Caribbean
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).
It has established in Washington, Snohomish Co., in the wetlands surrounding Meadow Lake, where natural outflow through the wetlands appears to be restricting spread down the drainage (pers. comm. J. Parsons, WA Dept. of Ecology, 2002).
Canada: Southeastern Ontario and adjacent western Quebec, including the Ottawa, Rideau and St. Lawrence Rivers and the shorelines of Lake Ontario and Lake Erie.
Ecology: Hydrocharis morsus-ranae is found in ponds and open marshes, and in bays and along quiet edges of lakes and rivers. It flowers from spring to fall, but most of its reproduction occurs asexually by spreading runners and production of resting bodies called turions or winter buds. These sink to the bottom and become dormant for the winter, then float to the surface and begin growing in spring (Environment Canada 2003).
Means of Introduction: Plant dispersal (aided by motor boats) through aquatic systems; entering from Canada, where in the 1930s it first escaped ornamental cultivation.
Status:
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).
Remarks:
References
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.
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). Available from: Canadian Wildlife Service.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.
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.
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.
Scribailo, R. W. and U. Posluzny. 1985. Floral development of Hydrocharis morsus-ranae (Hydrocharitaceae). American Journal of Botany 72(10): 1578-1589.
Other Resources:
Canada distribution and biological information at Canadian Wildife Service and National Botanical Services.
"European Frogbit: What is it? Should we be worried?" in Upwellings, Winter 2000, Michigan Sea Grant College Program.
NOAA Sea Grant Nonindigenous Species Site (SGNIS)
Author: C.C. Jacono
Contributing Agencies: 
NOAA - GLERL
Revision Date: 8/1/2002 Citation for this information:
C.C. Jacono. 2010. Hydrocharis morsus-ranae. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1110> Revision Date: 8/1/2002
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