Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Hydrocharis morsus-ranae



Hydrocharis morsus-ranae


  • Last modified
  • 19 November 2019
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Hydrocharis morsus-ranae
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Monocotyledonae
  • Summary of Invasiveness
  • H. morsus-ranae is a free-floating, stoloniferous aquatic plant that can grow to form dense floating mats of interlocking plants which cause many negative environmental and economic impacts. Some of these impacts include displacing na...

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Hydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.
CaptionHydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.
Copyright©Christian Fischer - CC BY-SA 3.0
Hydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.
HabitHydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.©Christian Fischer - CC BY-SA 3.0
Hydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.
CaptionHydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.
Copyright©Christian Fischer - CC BY-SA 3.0
Hydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.
HabitHydrocharis morsus-ranae (common frogbit or European frog's-bit); habit. North-eastern Lower Saxony, Germany.©Christian Fischer - CC BY-SA 3.0


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Preferred Scientific Name

  • Hydrocharis morsus-ranae Linnaeus, 1753

International Common Names

  • English: common frogbit; common frog-bit; European frog-bit; European frog's-bit; frogbit; frog-bit; frogs-bit; frog's-bit; Water frog-bit; water-poppy
  • French: grenouillete; hydrocharide grenouillette; hydrocharis des grenouilles; petit nénuphar

Local Common Names

  • Germany: Froschbiss
  • Italy: favagello di chiana; morso di rana
  • Netherlands: kikkerbeet

EPPO code

  • HYHMR (Hydrocharis morsus-ranae)

Summary of Invasiveness

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H. morsus-ranae is a free-floating, stoloniferous aquatic plant that can grow to form dense floating mats of interlocking plants which cause many negative environmental and economic impacts. Some of these impacts include displacing native plant species, reducing biodiversity, decreasing water quality and flow, clogging irrigation pumps, impeding recreational activities, and diminishing aesthetic value. H. morsus-ranae is extremely difficult and costly to control, and its ability to form new plants vegetatively has allowed it to spread and proliferate quickly (Scribailo and Posluszny, 1984). The trade and potential escape of H. morsus-ranae through the water garden industry plays a large role in its spread to new locations, as does the transportation of this plant on recreational equipment or by wildlife moving between water bodies (USDA-NAS, 2002; Catling et al., 2003). H. morsus-ranae is declared a noxious weed in parts of the United States (USDA-GRIN, 2002), and is currently established in New York, Vermont, Michigan, and Washington.  

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Monocotyledonae
  •                     Order: Hydrocharitales
  •                         Family: Hydrocharitaceae
  •                             Genus: Hydrocharis
  •                                 Species: Hydrocharis morsus-ranae

Notes on Taxonomy and Nomenclature

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The genus Hydrocharis (family Hydrocharitaceae) contains approximately 15-16 species (Diversity of Life, 2005; ZipcodeZoo, 2008). The genus name comes from the Greek hydro meaning ‘water’ and charis meaning ‘some sort of plant’. The specific epithet is derived from the Latin morsus meaning ‘bite’ and rana meaning ‘frog’, referring to the observation of frogs biting at the leaves, searching for caterpillars that make their protective envelopes from the plant (Catling et al., 2003). The English common name ‘frog-bit’ comes from this relationship. Hydrocharis morsus-ranae was first named by Linnaeus in 1753, and this is still its current accepted scientific name.


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H. morsus-ranae is a free-floating, stoloniferous herbaceous perennial aquatic plant that can grow to be 0.1-1.5 m across, with individual rosettes measuring 1-30 cm. H. morsus-ranae is mostly dioecious, though rarely both sexes can occur on the same rosette, albeit on different ramets within a genet (Scribailo and Posluszny, 1984). The roots are usually un-branched, unattached to the substrate, up to 50 cm long, and change colour from green to white as they develop and form numerous long root hairs. The stolons do not readily fragment, though winter buds (turions) are formed on the stolons in autumn, and are ellipsoidal to oval, 5-7 (-9) mm long with a distinct abscission layer. The leathery circular to heart shaped floating leaves are entire, have an indented (cordate) base, often dark purple underneath, are 1.2-6 cm long, 1.3-6.3 cm wide, and have a conspicuous aerenchyma on the undersurface near the mid-vein, with all veins arising from the base. The petioles are slender, 6-14 cm long, with two free lateral stipules up to 2.5 cm long at the petiole base.  
The flowers are unisexual, with the male flower arising from a spathe consisting of two bracts, each 1-1.2 cm long on a 0.7-5.5 cm long peduncle. The (1-) 2-5 flowers within each spathe have pedicels up to 4 cm long, white to greenish-white sepals 4-5.5 mm long, broadly obovate to orbicular white petals 9-19 mm long. It has 9-12 stamens, each 2-3.5 mm long in four whorls, with the two outer whorls being fully fertile, and the inner whorls sterile or partly sterile. The pollen is rounded, radiosymetric, without apertures and covered with spines.  
The female flowers are borne singly on peduncles up to 9 cm long, with greenish-white sepals 4-5 mm long, obovate to orbicular white-pinkish petals 10-15 mm long, staminodes simple, bifurcate or bifid; stigmas 6, up to 5 mm long, divided to 1/4 - 2/3 of their length. The seeds are approximately 1 mm long, transversely elliptic, covered with stout blunt processes, each with a spiral pattern on the outer surface (Cook and Lüönd, 1982).

Plant Type

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Seed propagated
Vegetatively propagated


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H. morsus-ranae is native through much of Europe and parts of temperate Asia (USDA-GRIN, 2002) as well as Africa (Catling et al., 2003). Cook and Lüönd (1982) define its native range as including western and central Europe, extending from Portugal, western France and the British Isles, north to southern Sweden and Finland, and south to northern Italy. There are scattered records in Eastern Europe to 40°E, while it is sparingly represented in Turkey, the Caucasus and south shore of the Caspian Sea. Isolated populations have also been reported from central Siberia and Kazakhstan (Cook and Lüönd, 1982). Reports of H. morsus-ranae from Australia and Japan (Holm et al., 1979) are unreliable and based upon material referable to H. dubia (Catling et al., 2003). H. morsus-ranae has declined or has been extirpated throughout parts of its European range, and is considered a conservation concern in several areas. In the United Kingdom, populations have decreased in their natural habitats, but populations have been reported in canals outside of its native range (Preston and Croft, 1997).  

In its non-native range, H. morsus-ranae is currently established in southeastern Canada, and it is known primarily from southeastern Ontario and western Quebec. It has also established in northern New York, northern Vermont, and southeastern Michigan in the eastern United States. H. morsus-ranae has also recently been reported as established in Washington, and is the first population recorded in the western coast of the United States (USDA-NAS, 2002).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 12 May 2022
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes


KazakhstanPresent, Few occurrencesNative
TurkeyPresent, Few occurrencesNative


Federal Republic of YugoslaviaPresentNative
NorwayPresent, LocalizedNativePopulation discovered in 1989 along a watercourse
-Eastern SiberiaPresentNative
-Western SiberiaPresentNative
SwitzerlandPresent, Few occurrencesNativeEndangered; specimens sent from the Zurich Botanical Gardens in 1932 to Canada.
United KingdomPresentNative

North America

CanadaPresentPresent based on regional distribution.
-OntarioPresentIntroduced1932Escape from hortcultural cultivation
United StatesPresent, Localized
-New YorkPresentIntroduced1974

History of Introduction and Spread

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The first recorded introduction of H. morsus-ranae into Canada was in 1932 when an intentional introduction for horticultural purposes was made at an aquatic pond in the arboretum of the Central Experimental Farm in Ottawa (CWS, 2003). Earlier introduction of the plant is also possible (Catling and Porebski, 1995). The original plants, or possibility seeds, came from the Zürich Botanical Garden in Switzerland (Dore, 1968; CWS, 2003). The population grew at the original site without incident until 1939, when Minshall (1940) noticed that it had spread to nearby sections of the Rideau Canal and Brown’s Inlet, a nearby artificial pond with underwater connections to the Canal. By 1952, a population was collected from the Ottawa River at Montreal Island, either as a result of floating plant material travelling and establishing downstream, or perhaps the result of a separate introduction from specimens which escaped confinement from the Montreal Botanic Garden or McGill University (Minshall and Scarth, 1952; Dore, 1968; Catling and Dore, 1982). In 1953 it had spread towards the exit of the Rideau Canal and along the shores of the Ottawa River, being found in the main channel of the Rideau River by 1957. During 1960 H. morsus-ranae was found at various locations along the Ottawa River around Montreal, as well as much further downstream at Lake St. Peter (CWS, 2003). By 1967 the plant had also spread upstream in the Rideau River to at least Merrickville (Dore, 1968), and continued to spread along the Rideau and Ottawa Rivers, as well as into connected tributaries and isolated wetlands (Reddoch, 1976). By 1970, the total extent of North American occurrence was a stretch of 340 km of major waterways (Catling and Dore, 1982). H. morsus-ranae was reported along the Lake Erie shoreline in 1976 (USGS-NAS, 2002). By 1980 it had extended southwest to Lake Ontario and northeast to Quebec City (Catling et al., 2003). H. morsus-ranae has recently continued to spread throughout much of southern Ontario.

H. morsus-ranae was first discovered in the United States in 1974 from the Oswegatchie River, just off the St. Lawrence River in northern New York (USGS-NAS, 2002). By the early 1980s, populations had spread and increased at several inland sites south of the St. Lawrence River, and into bays and marshes of Lake Ontario by the 1990s (Catling and Dore, 1982).


H. morsus-ranae was first discovered in Vermont during 1993 at the northern portion of Lake Champlain near the town of Grande Isle, and by 1999-2000 had spread to the southern portion of the lake near Benson, Orwell, and West Haven, Vermont, as well as Mill Bay in eastern New York (USDA-NAS, 2002).  


In Michigan, unidentified plants were first observed in 1996 during dredging of a slough at Lake St. Clair, and within two years the plants had become abundant throughout the marsh and formed dense mats in cut ponds. In 2000 the plants were identified as H. morsus-ranae, and established populations were observed in marshes of both the Detroit River and Lake St. Clair, both of which flow into Lake Erie (USDS-NAS, 2002).


H. morsus-ranae was first discovered in the western coast of the United States in 2001, where an established population was discovered in Snohomish County, Washington, in the wetlands surrounding Meadow Lake (USGS-NAS, 2002; Catling et al., 2003).


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Canada Switzerland 1932 Escape from confinement or garden escape (pathway cause); Horticulture (pathway cause) Yes USGS-NAS (2002) Plants or perhaps seeds came from the Zurich Botanical Garden, Switzerland.
USA Canada 1974 Interbasin transfers (pathway cause); Interconnected waterways (pathway cause) Yes USGS-NAS (2002)

Risk of Introduction

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H. morsus-ranae is continuing to expand its range and become more abundant. H. morsus-ranae is a popular water garden and aquarium plant, and the ability to order this plant over the Internet and through mail order gives it the ability to travel to all parts of the world (Catling et al., 2003). It has escaped confinement and has been intentionally or accidentally introduced on several occasions outside of its native range. In the locales to which it has been introduced, it has often become the dominant plant species, out-competing and displacing native species that depend on the ecosystem (Catling et al., 2003). The ability of H. morsus-ranae to reproduce vegetatively facilitates its spread and colonization; it is a highly competitive plant which is capable of a maximum rate of spread of 15.6 km/year, and has already spread over an area of 644 km from point of origin (Catling et al., 2003). Although its initial spread had been confined to interconnected waterways, it has since found ways to spread into isolated and unconnected wetlands and waterways, facilitated by dispersal on boats, trailers, and wildlife (Catling et al., 2003). Within the next ten to 20 years, it is anticipated that H. morsus-ranae will continue to move westward through the Great Lakes basin towards the Midwest, and become established in the northern Midwest and prairie regions of the United States (Catling and Porebski, 1995; Catling et al., 2003


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H. morsus-ranae prefers shallow, slow moving waters, inhabiting quiet edges of rivers, lakes, ponds, sheltered bays, open marshes, and wetlands (UFL-IFAS, 2002; USDA-NAS, 2002). It is also found growing in canals, beaver dams, swamps, and irrigation ditches. It tolerates a wide range of climatic conditions, and the genotypes established in North America also appear to have a broad tolerance. It is currently established in two major eco-zones of Canada and five eco-regions (Catling et al., 2003). Organic substrate is necessary for development, and it does not tolerate waters with a mineral substrate, such as clay pits of fishponds. H. morsus-ranae favours calcium-poor waters, often occurring on peaty soils, and often occurs in mesotrophic waters, though usually not found in oligotrophic conditions (Cook and Lüönd, 1982).  

Habitat List

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Terrestrial Natural / Semi-naturalRiverbanks Principal habitat Harmful (pest or invasive)
Terrestrial Natural / Semi-naturalWetlands Principal habitat Harmful (pest or invasive)
FreshwaterIrrigation channels Secondary/tolerated habitat Harmful (pest or invasive)
FreshwaterLakes Principal habitat Harmful (pest or invasive)
FreshwaterReservoirs Principal habitat Harmful (pest or invasive)
FreshwaterRivers / streams Principal habitat Harmful (pest or invasive)
FreshwaterPonds Principal habitat Harmful (pest or invasive)

Hosts/Species Affected

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Not applicable.

Biology and Ecology

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North American populations of H. morsus-ranae have a chromosome number of 2n=28 as reported by material collected by Dore and analyzed by G.A. Mulligan from the Rideau Canal in Ottawa, Ontario (Catling et al., 2003). Several other authors report 2n=28 for Eurasian material (Löve, 1980; Dvorak, 1989). H. morsus-ranae posses one pair of long sub-metacentric chromosomes, the rest being medium length, metacentric, acrocentric, or short metacentric (Cook and Lüönd, 1982). Meiosis is reported to be regular. Dvorak (1989) provides additional information on chromosome morphology.     

Reproductive Biology 

H. morsus-ranae reproduces primarily vegetatively by means of strong stolons and the productions of turion winter buds. It is estimated that a single plant can form approximately 100 to 150 turions (Dore, 1968; Scribailo and Posluszny, 1984).

H. morsus-ranae also has the ability to reproduce sexually, though reproduction by seeds is rarely reported (Catling et al., 2003), and probably is of limited importance in the spread of the species (Scribailo and Posluszny, 1984). The fruit is a globose berry containing up to 74 seeds, with an average of 26-42 seeds (Scribailo and Posluszny, 1985).   

Physiology and Phenology 

In late summer and early autumn, turions are formed along the stolon and then separate from the plant in late autumn, sinking towards the bottom where they remain dormant over winter for seven months (Dore, 1968). Their release from dormancy requires several weeks of chilling, with a temperature of approximately 5°C being optimal (ISSG, 2005). In the spring the turions rise towards the surface, germinate from late April to early May, and grow into small floating rosettes (Catling et al., 2003). Rosettes are well developed or fully grown by mid-May. By early June most plants have developed into three rosettes joined by stolons, and by mid to late June will often have six rosettes. Flowering is regulated by photoperiod, though it is very erratic and small fluctuations in temperature can readily influence timing. Generally, the peak flowering period in North America ranges from mid-July to mid-August. 


H. morsus-ranae is often associated with emergent and semi-emergent plants that offer protection from currents, wind, and waves, including: Typha spp., Phragmites australis, Sparganium spp., Lemna spp., Nymphaea spp., Hottonia inflate, Pontedaria cordata, Nuphar variegata, Butomus umbellatus, Sagittaria spp., Equisetum fluviatile, and Myriophyllum spp. (Catling et al., 2003).   

 In Canada, H. morsus-ranae also often occurs with Potamogeton pusillus, Potamogeton vaseyi, Spirodela polyrhiza, Utricularia vulgaris, and the exotic Lythrum salicaria (purple loosestrife) (CWS, 2003). 

Environmental Requirements 

H. morsus-ranae is found in waters with pH between 6.5-7.8 (Catling and Dore, 1982). It has been suggested that the mostly acid and nutrient poor waters of the Canadian Shield and northern Appalachian regions have restricted its spread (Catling and Porebski, 1995). Turions can tolerate only a brief period of freezing conditions, ranging from less than ten days to up to several weeks (Catling et al., 2003).  


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BW - Desert climate Tolerated < 430mm annual precipitation
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)

Soil Tolerances

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Soil reaction

  • neutral

Notes on Natural Enemies

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H. morsus-ranae is eaten by grass or amur carp (Ctenopharyngodon idella Val.), ducks, water birds, and rodents. It is a food plant for a number of insects and water snails (Catling and Dore, 1982), as well as host to a number of rusts, smuts and molds (Catling et al., 2003). In Europe it is reported as being consumed by beavers (Castor fiber) (Catling et al., 2003).    

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)

Hydrochory, the dispersal of disseminules by water currents, seems to be the main dispersal mode of vegetative fragments within a watershed.  

Vector Transmission (Biotic)

H. morsus-ranae can be transported with wildlife and carried to new locations. Dispersal by water birds is suggested as the vector of dispersal of newly discovered populations in Norway (Halvorsen, 1989). Great blue herons (Ardea herodias) have been observed flying distances of 2 km with interlocking plants of H. morsus-ranae attached to their feet (Catling et al., 2003).  

Accidental Introduction

H. morsus-ranae
can be spread accidentally to new locations by the movement of boats, trailers, nets, sea planes, and other recreational equipment between water bodies (USDA-NAS, 2002). Taking plants from an existing wetland in order to restore another wetland may also possibly introduce exotic species to a new location (Catling et al., 2003). H. morsus-ranae can also be a ‘hitchhiker’ plant with other species ordered through water garden catalogues. Plants can alsobe accidentally introduced to new locations by ornamental ponds flooding into surrounding natural waterways. In addition, it is possible that H. morsus-ranae has been introduced through hobbyists emptying unwanted aquarium species directly into surrounding waterways.

Intentional Introduction

The trade of this plant as an aquarium plant through the Internet and mail order has greatly increased its availability and ease of spread into new environments. In addition, some new colonies of H. morsus-ranae may have been started intentionally by duck hunting clubs, which introduced the plant to provide food and cover for waterfowl (Catling and Dore, 1982).


Impact Summary

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Cultural/amenity Positive and negative
Economic/livelihood Negative
Environment (generally) Positive and negative

Economic Impact

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H. morsus-ranae has limited water flow in irrigations systems and canals (Catling et al., 2003). In addition, the loss of recreational and aesthetic value associated with H. morsus-ranae can also cause a decline in waterfront property values, as well as possible declines in tourism related revenue for the community.

Environmental Impact

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Impact on Habitats

The dense floating mats of vegetation that are characteristic of this species when introduced outside of its native range can block light penetration in the water column, reducing the available light for native aquatic vegetation (Catling et al., 2003). H. morsus-ranae can also deplete oxygen levels by limiting water circulation and through increased decomposition of dead plants. Dense mats of H. morsus-ranae also have the ability to change water hydrology and quality, negatively affecting the ecosystem in which it occurs.

Impact on Biodiversity

H. morsus-ranae
reduces biodiversity by competing with and displacing native vegetation, and is capable of changing the fauna and flora of an ecosystem.H. morsus-ranae can form dense monocultures which exclude light to native plants and do not provide habitat or food for wildlife. Very dramatic declines in the cover value of native submerged aquatic vegetation were noted under mats of H. morsus-ranae (Catling et al., 1988). H. morsus-ranae restricts available nutrients and dissolved gases for other plants, inhibiting plant growth beneath the mats. Large decomposing mats of H. morsus-ranae also have the ability to deplete dissolved oxygen levels, which can potentially cause fish and other aquatic organism kills (Catling et al., 2003).


Social Impact

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H. morsus-ranae can form dense mats that impede recreational activities such as boating, fishing, swimming, water skiing, canoeing, and kayaking. In addition, unsightly mats of vegetation decrease aesthetic values. These declines in recreational and aesthetic values can decrease tourism, which can be a major source of livelihood within the community. 

Risk and Impact Factors

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  • Proved invasive outside its native range
  • Has a broad native range
  • Highly adaptable to different environments
  • Highly mobile locally
  • Fast growing
  • Has high reproductive potential
  • Gregarious
  • Has propagules that can remain viable for more than one year
  • Reproduces asexually
  • Has high genetic variability
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Modification of hydrology
  • Modification of natural benthic communities
  • Modification of nutrient regime
  • Monoculture formation
  • Negatively impacts cultural/traditional practices
  • Negatively impacts livelihoods
  • Negatively impacts aquaculture/fisheries
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
  • Transportation disruption
Impact mechanisms
  • Competition - monopolizing resources
  • Competition - shading
  • Rapid growth
  • Rooting
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally deliberately
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field


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Economic Value

Ornamental plants of H. morsus-ranae are sold for water ponds, though the specific economic value of this particular species in the ornamental plant trade is undocumented.

H. morsus-ranae plant material collected in June had crude protein levels of 22-24%, suggesting a potential value as a forage and compost (Catling et al., 2003).

Social Benefit

H. morsus-ranae
has also been proved beneficial as an experimental plant for physiological and developmental studies because of its large, clear unicellular root hairs, ease of cultivation, and regular organogenesis (Catling et al., 2003).

Environmental Services

H. morsus-ranae
is a food plant for several species of water birds, rodents, fish, and insects (Catling et al., 2003). In association with other aquatic vegetation, it can provide some cover for insects and fish (Nichols and Shaw, 1986). H. morsus-ranae may also be beneficial in removing nitrogen and phosphorus from wastewater (Reddy, 1984). 


Uses List

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Animal feed, fodder, forage

  • Fodder/animal feed
  • Forage
  • Invertebrate food


  • Wildlife habitat


  • Botanical garden/zoo
  • Laboratory use
  • Pet/aquarium trade
  • Research model
  • Sport (hunting, shooting, fishing, racing)

Detection and Inspection

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Infestations of aquatic invasive species are often first reported at boat launches, and these areas should be monitored frequently in order to eradicate or control new invasions at an early stage. Users should inspect all recreational equipment before leaving any water body, and any visible plants, animals, or sediment should be removed. In addition, rinsing gear with hot water or steam may help in removing any additional non-visible organisms. 

Similarities to Other Species/Conditions

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H. morsus-ranae looks similar to Limnobim spongia, commonly referred to as American frog-bit (UFL-IFAS, 2002). H. morsus-ranae can be distinguished from L. spongia by having relatively less developed aerenchyma on the undersurface of the leaf, relatively longer leaf lobes, leaf veins on either side of the mid-vein less ascending, free stipules in pairs, roots usually un-branched, and stolon buds developing one instead of multiple roots initially (Catling and Dore, 1982). 

 H. morsus-ranae may also be confused with other round, floating leaves plants such as Nymphaea spp., Nuphar spp., and Brascenia schrebii. H. morsus-ranae differs from these aquatics by having rounded leaves with five prominent veins and converging primary veins. H. morsus-ranae seedlings may be distinguished from the floating duckweeds Lemna minor and Spirodela polyrhiza by its roots, which arise from a rosette base or base of a leaf petiole rather than directly from the undersurface of the leaf (Catling et al., 2003).   

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.


As with all weed management, prevention is better and more cost-effective than control.

Rapid response

Early detection and eradication are essential in the prevention of future invasions and spread of H. morsus-ranae. Smaller, localized populations have better success at being controlled than those which have the opportunity to spread and become well established (Catling et al., 2003). 

Public awareness

Several publications have been produced in areas with H. morsus-ranae populations regarding the impacts of invasive species such as H. morsus-ranae, and the steps that lake recreationists need to take in order to prevent introducing and spreading aquatic invasives.


Cultural control and sanitary measures

In several regions where aquatic invasives have established, governmental organizations have started requiring that recreationists drain all water and clean off all gear (boats, trailers, fishing equipment, etc.) used on water bodies in order to minimize the chance of spreading aquatic invasive species, such as H. morsus-ranae, to other areas.

Physical/mechanical control

Past control of H. morsus-ranae has been primarily by means of mechanical removal. Small scale raking by hand in the spring can provide a temporary solution, and should be done after over-wintering turions have initiated growth on the water surface, but before dense mats have developed (Catling et al., 2003).

In small ponds, H. morsus-ranae may be controlled by a water drawdown either over winter or in late May to early June, when turions have already germinated, but before extensive summer growth has begun (Catling et al., 2003).

Movement control

Several countries have banned the importation or sale of exotic plants, such as H. morsus-ranae in attempts to minimize the chance of introduction to non-native regions.

Biological control

Grass carp, Ctenopharyngodon idella , will readily feed on H. morsus-ranae, though theintroduction of grass carp can negatively impact the coexisting native submerged vegetation, and introduction is even prohibited in some countries.

Chemical control

H. morsus-ranae is susceptible to the herbicides diquat, Paraquat™, chlorthiamid, and cyanatryn (Newbold, 1977). The first three listed chemicals are most efficient in non-flowing waters, and work to change the plant community structure and reduce species diversity rather than eradicating all plant life. Cyanatryn can be used in flowing water in the form of a slow-release granule. Breakdown of the herbicides in water generally occurs after 2-11 days, depending on bacterial presence and sometimes light (Newbold, 1975; Catling et al., 2003).


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Catling PM; Dore WG, 1982. Status and identification of Hydrocharis morsus-ranae and Limnobium spongia (Hydrocharitaceae) in northeastern North America. Rhodora, 84(840):523-545.

Catling PM; Mitrow G; Haber E; Posluszny U; Charlton WA, 2003. The biology of Canadian weeds. 124. Hydrocharis morsus-ranae L. Canadian Journal of Plant Science, 83(4):1001-1016.

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Cook CDK; Luond R, 1982. A revision of the genus Hydrocharis (Hydrocharitaceae). Aquatic Botany, 14(2):177-204.

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Dore WG, 1968. Progress of the European frog-bit in Canada. The Canadian Field-Naturalist, No. 82:76-84.

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Halvorsen R, 1989. Hydrocharis morsus-ranae in Skien Telemark Norway. Blyttia, 41(1):45-48.

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Löve A, 1980. Chromosome Number Reports LXIX. Taxon, No. 29:1-98.

Minshall WH, 1940. Frog-bit Hydrocharis morsus-ranae L. at Ottawa. The Canadanian Field-Naturalist, No. 54:44-45.

Minshall WH; Scarth GW, 1952. Effect of growth in acid medium on frog-bit root cells. Canadian Journal of Botany, No. 30:188-208.

Newbold C, 1975. Herbicides in aquatic systems. Biological Conservation, 7(2):97-118.

Newbold C, 1977. Aquatic herbicides: possible future developments. Linn. Soc. Symp. Ser. Vol. Linn. Soc. Symp. Ser, No. 5:119-131.

Nichols SA; Shaw BH, 1986. Ecological life histories of the three nuisance plants, Myriophyllum spicatum, Potamogeton crispus and Elodea Canadensis. Hydrobiologia, No 131:3-21.

Preston CD; Croft JM, 1997. Aquatic plants in Britian and Ireland. Colchester, England: Harley Books, 365 pp.

Reddoch A, 1976. European frog-bit - a progress report. Trail and Landscape, No. 10:87-89.

Reddy K, 1984. Nutrient removal potential of aquatic plants. Aquatics, No. 6:15-16.

Sager L; Clerc C, 2006. Factors influencing the distribution of Hydrocharis morsus-ranae L. and Rumex hydrolapthum Huds. in a mowed low-lying marshland. Hydrobiologia, No. 570:223-229.

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Distribution References

CABI, Undated. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI

Canadian Wildlife Service, 2003. European frog-bit (Hydrocharis morsus-ranae). In: European frog-bit (Hydrocharis morsus-ranae), Canada: Canadian Wildlife Service.

Catling P M, Mitrow G, Haber E, Posluszny U, Charlton W A, 2003. The biology of Canadian weeds. 124. Hydrocharis morsus-ranae L. Canadian Journal of Plant Science. 83 (4), 1001-1016.

Cook C D K, Luond R, 1982. A revision of the genus Hydrocharis (Hydrocharitaceae). Aquatic Botany. 14 (2), 177-204. DOI:10.1016/0304-3770(82)90097-3

EPPO, 2022. EPPO Global database. In: EPPO Global database, Paris, France: EPPO. 1 pp.

Halvorsen R, 1989. Hydrocharis morsus-ranae in Skien Telemark Norway. Blyttia. 41 (1), 45-48.

Invasive Species Specialist Group, 2005. Hydrocharis morsus-ranae. In: Global Invasive Species Database, University of Auckland, Aukland, New Zealand: Invasive Species Specialist Group, IUCN.

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

USA, USDA-GRIN, 2002. Hydrocharis morsus-ranae. In: Germplasm Resources Information Network (GRIN), Beltsville, Maryland, USA: National Germplasm Resources Laboratory.

USGS-NAS, 2002. Hydrocharis morsus-ranae. In: United States Geological Survey - Nonindigenous Aquatic Species,


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01/07/08 Original text by:

Alison Mikulyuk, Wisconsin Dept of Natural Resources, Science Operations Center, 2801 Progress Rd, Madison, WI 53716, USA

Michelle Nault, Wisconsin Department of Natural Resources, 2801 Progress Rd, Madison, WI 53716-3339, USA

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