Elodea canadensis (Canadian pondweed)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Water Tolerances
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Economic Impact
- Environmental Impact
- Social Impact
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Elodea canadensis Michx.
Preferred Common Name
- Canadian pondweed
Other Scientific Names
- Anacharis alsinastrum Bab. ex Planch
- Anacharis canadensis (Michx.) Planch.
- Anacharis iowensis (Wylie) Wylie
- Anacharis linearis (Rydb.) Vict.
- Anacharis occidentalis (Pursh) Vict.
- Anacharis planchonii (Casp.) M.Peck
- Anacharis pomeranica Peterm.
- Apalanthe schweinitzii Planch.
- Elodea brandegeeae H.St.John
- Elodea gigantea J.K.Santos
- Elodea ioensis Wylie
- Elodea latifolia Casp.
- Elodea linearis (Rydb.) H.St.John
- Elodea oblongifolia Michx. ex Casp.
- Elodea planchonii Casp.
- Elodea schweinitzii (Planch.) Casp.
- Hydora canadensis (Michx.) Besser
- Philotria angustifolia (Muhl.) Britton ex Rydb.
- Philotria canadensis (Michx.) Britton
- Philotria iowensis Wylie
- Philotria linearis Rydb.
- Philotria planchonii (Casp.) Rydb.
- Serpicula canadensis (Michx.) Eaton
- Udora canadensis (Michx) Nutt.
International Common Names
- English: American duckweed; American waterweed; Canadian elodea; Canadian pondweed; Canadian waterweed; common elodea; ditch weed; elodea; oxygen weed; water thyme; waterweed; yankee weed
- Spanish: broza del Canada; elodea; peste de las aguas
- French: élodée d'Amérique; élodée du Canada; peste-d'eau
- Portuguese: elodea; espiga-de-água; estrume-novo
Local Common Names
- Cuba: elodea
- Denmark: almindelig vandpest
- Estonia: Kanada vesikakt
- Germany: Kanada-Wasserpest; Kanadische Wasserpest
- Italy: elodea; elodea; peste d'acqua; peste d'acqua comune
- Japan: kanadamo
- Latvia: Kanādas elodeja
- Lithuania: kanadinė elodėja
- Netherlands: brede waterpest; waterpest
- Norway: vasspest
- Poland: moczarka kanadyjska
- Romania: ciuma apei; ciuma apelor; lipitoare
- Serbia: kanadska vodena kuga
- Slovakia: vodomor kanadský
- Slovenia: vodna kuga
- South Africa: Kanadese waterpes
- Sweden: vattenpest
- ELDCA (Elodea canadensis)
Summary of InvasivenessTop of page
Elodea canadensis is a submerged aquatic plant of slower flowing rivers, native to North America. It has been intentionally introduced into areas outside of its native range as an ornamental aquarium species. This species has a wide ecological tolerance and grows relatively fast. It is a perennial, overwintering in the deeper water, and reproducing asexually. Disturbance increases the dispersal of numerous propagules and the vigorous re-growth is enhanced through changes in availability of nutrients. E. canadensis can form dense mats which can interfere with recreational activities, navigation and port infrastructure. In addition to this, the dense mats outcompete native plant species and therefore decrease the biodiversity in an area. It also accentuates the accumulation of finer organic silts which enhances its growth further as nutrients are released. E. canadensis is considered invasive in Australia, New Zealand, Cuba, Alaska and the majority of European countries where it is present. Control is complicated and loss of fragments should be minimized to prevent further spread. It is included in the IUCN Red List, categorized as being of Least Concern. Thus, no conservation action is proposed or is necessary for this species.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Monocotyledonae
- Order: Hydrocharitales
- Family: Hydrocharitaceae
- Genus: Elodea
- Species: Elodea canadensis
Notes on Taxonomy and NomenclatureTop of page
Historically there has been much confusion in the classification of the species of the genus Elodea (Family Hydrocharitaceae). However, Cook and Urmi-König (1985), in the latest revision of the genus, recognize five species of Elodea, all of them from the New World: E. potamogeton (Bert) Espinosa and E. callitrichoides (Rich.) Caspary are endemic to South America, while E.bifoliata St. John, E. canadensis and E. nuttallii grow in North America.
The name Elodea canadensis Michx. is universally accepted for this common, widespread waterweed. Four varieties are recognized by Missouri Botanical Garden (2019): var. angustifolia (Muhl.) Farw., var. gigantea Hort. In Bailey, var. latifolia (Casp.) Asch. & Graebn and var. planchonii Farw. ITIS (2014), however, does not recognize any of these.
DescriptionTop of page
Elodea canadensis is a dioecious, perennial, submerged aquatic macrophyte with elongated flexuous stems and long internodes which are clothed with whorls of sessile, minutely-serrate leaves and rooted from their nodes, typically in mud substrates. The middle and upper leaves, typically three per whorl, are elliptic, approximately 2-5 mm wide; leaves in the upper whorls grow closely together. Male flowers are pedunculate by the elongate, filiform base of the floral tube, not released from the plant at anthesis; sepals 3.5-5.0 mm long, petals 5 mm long. The staminate spathe has a pedunculate base, inflated, 7 mm long, 4 mm wide. The female flower stalk is approximately 15 cm long; sepals and petals 2-3 mm long. Petals white. Pistillate spathe cylindrical. A full description is provided by eFloras (Flora of North America Editorial Committee, 2018).
DistributionTop of page
Elodea canadensis originates from North America, concentrated around the St Lawrence Valley and the Great Lakes regions and the Pacific West Coast (Bowmer et al., 1995), but now occurs throughout the USA. The plant was introduced to the UK in the mid-1800s and has spread eastwards through Western Europe with the apparent exception, so far, of Iberia and northern Scandinavia. It is considered an invasive plant in Europe and has been reported as one of the most widespread invasive species in Russia (Vinogradova et al., 2018). E. canadensis is widespread and abundant in New Zealand (Bowmer et al., 1995) and is ranked as a medium risk with a weed potential score of 46 in New Zealand by the Aquatic Weed Risk Assessment Model (AWRM) (Champion et al., 2007). It has become naturalized in water bodies in the south-eastern parts of Australia, particularly in areas near major cities. It is most common in southern and eastern New South Wales, Victoria and Tasmania. It is also recorded from south-eastern South Australia and is sparingly naturalized in south-eastern Queensland (EWA, 2016). It has been recorded in only a few Asiatic and Latin American countries.
Elodea canadensis is included in the IUCN Red List, categorized as being of Least Concern. Thus, no conservation action is proposed or is necessary for this species (Maiz-Tome, 2016)
Distribution TableTop of page
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: 25 Feb 2021
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|South Africa||Present, Widespread||Introduced|
|Federal Republic of Yugoslavia||Present||Introduced|
|Finland||Present||Introduced||Extremely common in southern and central Finland and still expanding its range|
|United Kingdom||Present, Widespread||Introduced||Invasive||First reported in Scotland in 1854|
|Canada||Present||Present based on regional distribution.|
|-British Columbia||Present, Widespread|
|United States||Present||Present based on regional distribution.|
|-New Hampshire||Present, Widespread||Native|
|-New Jersey||Present, Widespread||Native|
|-New Mexico||Present, Widespread||Native|
|-New York||Present, Widespread||Native|
|-North Carolina||Present, Widespread||Native|
|-North Dakota||Present, Widespread||Native|
|-Rhode Island||Present, Widespread||Native|
|-South Carolina||Present, Widespread|
|-South Dakota||Present, Widespread||Native|
|-West Virginia||Present, Widespread||Native|
|-New South Wales||Present, Widespread||Introduced|
|New Zealand||Present, Widespread||Introduced|
History of Introduction and SpreadTop of page
The first authenticated observation of E. canadensis in Europe was of a well-established population in Ireland in 1836, although unconfirmed reports of the weed in the British Isles date as far back as 1817 (Simpson, 1984). It has since been introduced to other European countries: first reported in Scotland in 1854, and in Germany and Poland in 1859. E. canadensis then spread to Scandinavia, where it was reported in Denmark in 1870 and Sweden in 1871. It was intentionally planted in the Botanical Garden of the University of Helsinki, Finland in 1884, and subsequently spread into the entire country (Josefsson, 2011). In Italy E. canadensis was recorded for the first time in 1891 in the Veneto region, probably as an escape from the Botanic Garden of Padua, where it was introduced intentionally (Brundu, 2015).
Elodea canadensis was observed for the first time in the European part of Russia in St Petersburg in 1880 and the Caspian Sea in 1895 (Bazarova and Pronin, 2010), in Latvia in 1872, in Lithuania in 1884 and in Estonia in 1905 (Josefsson, 2011). In Croatia it was recorded for the first time in 1894 in Ješkovo pond in Gola, Podravina (Nikolić, 2018). E. canadensis was first observed in Norway near Oslo in 1925, but only began to spread to other areas of the country in the 1960s (Josefsson, 2011). Later, at the end of the 1970s it was recorded in Lake Baikal (Kozhova and lzhboldina, 1993). It is now widespread in north and central European countries. E. canadensis was introduced in Australia (Tasmania) in 1876 (Council of Heads of Australasian Herbaria, 2014) and in New Zealand in 1868 (Chapman, 1970).
Invasion and spread were most rapid during the 19th century and many populations, particularly in the UK, have now stabilized. Dramatic increases have been rare since the start of the 20th century (Millane and Caffrey, 2014), by which time it was considered to be abundant and occurring in all suitable waters (Simpson, 1984). By the middle of the last century, it seems to have reached the maximum extent of its distribution (Simpson 1986, 1990; UK, Joint Nature Conservation Committee, 1995). Since that time, E. canadensis populations appear to have stabilized (Simpson, 1984; Simpson and Duenas, 2011), or declined, and in some cases disappeared (Millane and Caffrey, 2014). The introduction of the closely related and invasive E. nuttallii into Europe resulted in the displacement of E. canadensis from many localities in its introduced range where it had become well established (Simpson, 1990; Thiébaut et al., 1997; Barrat-Segretain, 2001; Larson, 2007a; Duenas, 2010). The displacement often occurs over a relatively short time, in one or two years (James et al., 1999). It has been suggested that both global warming and accelerated eutrophication may explain the reduced spread of E. canadensis in Europe in recent decades (Kolada and Kutyła, 2016).
Recently, it has been recorded as a frequent species in the Bashkortostan Republic, Russia (Golovanov et al., 2018). Its presence has also been confirmed in the transboundary lake, Great Prespa, in Greece (Poulis and Zervas, 2017).
IntroductionsTop of page
|Introduced to||Introduced from||Year||Reason||Introduced by||Established in wild through||References||Notes|
|Natural reproduction||Continuous restocking|
|Australia||1876||Yes||No||Council of Heads of Australasian Herbaria (2014)||First recorded in Tasmania|
|Ireland||North America||1836||Yes||No||Josefsson (2011)|
|New Zealand||1868||Aquaculture (pathway cause)||Yes||No||Thomson (1922)|
Risk of IntroductionTop of page
Elodea canadensis has been intentionally introduced outside its natural range via trade in live aquarium plants, and has spread by escaping from garden ponds and during the disposal of garden waste near waterways. E. canadensis populations appear to have stabilized (Simpson 1984; Simpson and Duenas, 2011) and declined. In some cases, it has disappeared (Millane and Caffrey, 2014) or has been replaced by other invasive aquatic plants. This species is sold commercially as an aquarium or garden plant, and there is a high risk of introduction. New invasions are still occurring in some parts of Europe (Poulis and Zervas, 2017).
Elodea canadensis is included on the black lists of certain European countries: Belgium (Branquart et al., 2010), Germany (Verbrugge et al., 2012). In the UK it is listed as a wild invasive non-native plant in Schedule 9 of the Wildlife Act (England and Wales) because of its high environmental risk. Further introductions in these regions are therefore unlikely.
HabitatTop of page
Elodea canadensis can grow in a range of habitats, but prefers quiet ponds, lakes and slow-moving water with peaty or muddy silt substrates. E. canadensis is a common species in nutrient rich, or eutrophic, relatively quiet or slower water flows of many inland freshwater bodies (ponds, lakes, ditches, irrigation channels; McGavigan, 2017) and is often associated with organic-rich muds. It can occur in fast-flowing waters but only at low abundance (Lansdown, 2015).
Habitat ListTop of page
|Terrestrial||Natural / Semi-natural||Wetlands||Secondary/tolerated habitat||Productive/non-natural|
|Freshwater||Irrigation channels||Principal habitat||Harmful (pest or invasive)|
|Freshwater||Rivers / streams||Principal habitat||Productive/non-natural|
|Freshwater||Ponds||Principal habitat||Harmful (pest or invasive)|
Biology and EcologyTop of page
Chromosome number 2n = 24 (Preston and Croft, 1997). For further information on chromosome counts, see Missouri Botanical Garden (2018). Some plastid and chloroplast sequences are available for this species, found in the GenBank database (see list in Atlas of Living Australia, 2018). Only a single haplotype has been found in the introduced range of this species, which is the most widespread haplotype in the native range. Therefore, it has not yet been possible to determine the geographic origin, size or number of introductions (Huotari and Korpelainen, 2013). Although E. canadensis has low genetic diversity in its non-native range, as would be expected in a clonal species, some populations of E. canadensis in New Zealand showed higher levels of genetic structure than more recently introduced invasive species, which can be attributed to mutations accumulating post-introduction (Lambertini et al., 2010). This pattern of genetic variation has also been detected in Finland (Huotari et al., 2011). Phylogenetic analysis of the chloroplast genome of E. canadensis supports the placement of this species as a basal monocot (Huotari and Korpelainen, 2012).
Elodea canadensis is dioecious and male plants are less common than female in its native range. Only female plants are currently found in Europe, and male plants have not been reported since 1903 (Cook and Urmi-König, 1985), so reproduction is only vegetative, involving vegetative fragments and turions (overwintering buds). Very small plant fragments are able to form roots from nodes and start growing (McGavigan, 2017). The main growing season is between mid-April and October. Plants die back in Autumn. Turions or short, densely-leaved resistant stems, develop then break off to float around the water body before they sink to the bottom over winter, where they rest until they re-grow in spring (Millane and Caffrey, 2014).
Over-wintering buds and fragments of the brittle branches are easily detached by waves, currents, foraging animals and boat traffic. New roots develop quickly on the nodes of these fragments which are carried downstream to form new stands. This method of propagation gives E. canadensis a considerable advantage over annual species and resulted in its rapid spread throughout Europe following its introduction from North America (Holm et al., 1997; Josefsson, 2011).
Physiology and Phenology
Perennation is by densely-leaved crowded apices or turions. During autumn, apices cease to elongate and come to bear tightly clustered dark green leaves, which contain increased starch and are slightly more cuticularized than the normal foliage leaves. These apices may be liberated when the parent stems disintegrate and sink to the bottom, or remain attached throughout winter. The apices remain dormant until spring, when the leaves expand, adventitious roots develop from the lower nodes, the axis elongates and a new plant is formed. E. canadensis begins to grow during the spring season in temperate zones as the temperature rises to between 10-15°C. At ambient light levels, shoot biomass increases with temperature up to 28°C; root biomass shows an opposite tendency (Barko et al., 1982). Growth of this species is greatly stimulated under eutrophic conditions (Hughes, 1976; Barko and Smart, 1983; Krausch, 1987).
Erhard and Gross (2006) suggested that the production of allelochemicals that interfere with the growth of cyanobacteria and algae by both E. canadensis and the closely related E. nuttallii could play at least some role in the success of these two species as invasive species.
Evidence shows that this plant is very adaptable and has can spread under a wide range of conditions and nutrient concentrations ranging from oligotrophic to eutrophic (Cook and Urmi-König 1985; Simpson, 1990). E. canadensis has a wide climatic tolerance (it is present from Alaska to Puerto Rico), though it may be less common at the extremes of its range, being predominant in temperate areas of North America and Europe. In studies of maximum depths at which a number of submerged aquatic plants were found, the maximum recorded for any species was 12-14 m for Elodea (Sheldon and Boylen, 1977; Pip and Simmons, 1986; Wells et al., 1997). Its average height is about 1.2 m, having a maximum height of 2.5 m (Wells et al., 1997). In Europe it can survive in water depths of up to 4 m (McGavigan, 2012) in slow moving water. This species can survive and even grow slowly under ice cover (Bowmer et al., 1995). In North America it has been recorded in neutral to slightly alkaline inland waters and in fresh to slightly brackish coastal waters (Holm et al., 1997).
Riis et al. (2012), compared the effects of temperature and light availability on the growth and morphology of E. canadensis, Egeria densa and Lagarosiphon major and suggested that, in general, subject to variations due to timing of introductions, E. densa will dominate warmer, shallower waters, L. major will dominate in colder, clear-water lakes, whilst E. canadensis will continue its role as a pioneer species which is rapidly replaced by the two taller species after their arrival.
Elodea canadensis prefers clean water with a current from 0 to 1 m/s. Optimum water temperatures range from 10 to 20°C, and silty water or water with organic sediment is preferred to a sandy substrate (Bowmer et al., 1995, Barrat-Segretain et al., 2002). The habitat preference of E. canadensis in lakes is towards large and deep lakes located at high altitudes, with long water-retention times and high water quality (Kolada and Kutyła 2016). E. canadensis exhibits positive growth under experimental conditions of high‐salt concentrations (Stoler et al., 2018). Consequently, salt marshes and brackish waters are likely to be invaded by this species if salt concentration is lower than to 3 g/l of salt (Thouvenot and Thiébaut, 2018).
ClimateTop of page
|C - Temperate/Mesothermal climate||Preferred||Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C|
|Cf - Warm temperate climate, wet all year||Tolerated||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|
|Cw - Warm temperate climate with dry winter||Preferred||Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)|
|A - Tropical/Megathermal climate||Tolerated||Average temp. of coolest month > 18°C, > 1500mm precipitation annually||It has been introduced in a few tropical countries|
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Absolute minimum temperature (ºC)||-1||4|
Water TolerancesTop of page
|Parameter||Minimum Value||Maximum Value||Typical Value||Status||Life Stage||Notes|
|Conductivity (µmhos/cm)||200||1000||Optimum||2000 tolerated|
|Depth (m b.s.l.)||1||Optimum||3 (-12) tolerated|
|Dissolved oxygen (mg/l)||Optimum||metabolism creates range of 40-250%|
|Hardness (mg/l of Calcium Carbonate)||20||300||Optimum||<20 - >400 tolerated|
|Salinity (part per thousand)||0||Optimum||0.05 seawater tolerated|
|Velocity (cm/h)||0||700||Optimum||0-20 cm/sec|
|Water pH (pH)||7||8.5||Optimum||8.5-10 tolerated|
|Water temperature (ºC temperature)||10||25||Optimum||4-28 tolerated but probably temperature adaptive|
Notes on Natural EnemiesTop of page
The snails Lymnaea peregra [Radix peregra] and Bithynia spp. are natural herbivores of E. canadensis. Populations of this species can expand enormously if not controlled by natural predators and under such circumstances snails can serve as a biological control agent. However, Pieczynska (2003) studied the damage inflicted on a population of E. canadensis by the snail Lymnaea stagnalis and concluded that although the snail caused a substantial reduction in biomass and severe damage to E. canadensis, the plant fragments remaining after grazing showed a high capacity to regenerate new plants. Hygraula nitens is a New Zealand native moth with aquatic larvae that feed on submerged aquatic plants. Some experimental mesocosm studies showed larvae had a major effect on E. canadensis along with other non-native macrophytes as Hydrilla verticillata, Ceratophyllum demersum, Lagarosiphon major and Egeria densa (Redekop et al., 2018).
Means of Movement and DispersalTop of page
Elodea canadensis can easily be spread by the transport of boats and equipment between waterbodies. Seasonal flooding can also result in the spread of the organism locally (Barrat-Segretain and Elger, 2004). Fragments have high survival rates which allow them to be dispersed over long distances. Relative to other macrophytes such as Egeria densa and Lagarosiphon major, E. canadensis produces a greater number of fragments, which are longer and have a greater regenerative capacity (Redekop et al., 2016).
Vector Transmission (Biotic)
Pieces of fragment may become attached to aquatic animals, mammals, fish or birds (Josefsson, 2011) and be transferred locally.
Accidental spread of Elodea canadensis may occur via attachment of fragments to fishing equipment and boats (Kozhova and Izhboldiana, 1993; Mjelde et al., 2012). When it was first observed in Europe, in Ireland in 1836, it was suggested that one of the pathways of introduction could be through timber-trade commodities (Marshall, 1852 and 1857 in Brundu, 2015). As the timber in that time used to be transported as rafts in rivers, it could have picked up some fragments of the plants. Nowadays, it is highly unlikely that this sort of pathway still exists
Elodea canadensis was intentionally introduced into countries outside of its native range as an ornamental aquarium species via the trade in live aquarium plants, legal or otherwise (Bowmer et al., 1995) and via its disposal in nearby waterways.
Pathway CausesTop of page
|Fisheries||Yes||Kozhova and Izhboldiana; 1993|
|Flooding and other natural disasters||Yes||Barrat-Segretain and Elger; 2004|
|Garden waste disposal||Yes||Bowmer et al.; 1995|
|Internet sales||Yes||Millane and Caffrey; 2014|
|Ornamental purposes||Yes||Yes||Bowmer et al.; 1995|
|Pet trade||Yes||Yes||Bowmer et al.; 1995|
Pathway VectorsTop of page
|Aquaculture stock||Fragments with stocking/or nets||Yes||Yes||Bowmer et al.; 1995|
|Floating vegetation and debris||Erratic, flood events||Yes||Barrat-Segretain and Elger; 2004|
|Land vehicles||On wheels, tracks or in attached mud etc.||Yes||Barrat-Segretain and Elger; 2004|
|Pets and aquarium species||Casual introductions and discarded material||Yes||Bowmer et al.; 1995|
|Water||Yes||Barrat-Segretain and Elger; 2004|
|Ship hull fouling||Yes|
Economic ImpactTop of page
Both E. canadensis and the closely related E. nuttallii have the potential to develop into dense submerged beds. This prevents the use of water for recreational and professional purposes (Larson, 2003), and disrupts navigation and port infrastructure (CPS-SKEW, 2008). The plant can also clog and impede drainage waterways. Water flow in irrigation channels may slow and become blocked, reducing water supply to irrigation fed crops, such as rice in Asiatic countries and cotton in the USA. In Australia, Elodea is one of the main problems in 8000 km of canals and irrigation channels which feed the farm areas of Victoria (Bill, 1969). Mehta et al. (1973) reported that about 1500 ha of the Chambal irrigation system in India was infested with aquatic weeds, causing a reduction in the water carrying capacity by as much as 80%. Elsewhere, infestations have been reported to reduce water flow in canals and streams by up to 80%. This in turn may interfere with water traffic, disturb hydroelectric and urban water supplies, limit recreational water use and change the aquatic environment. Blockage of larger channels may inhibit ship movements, thus affecting trade. Submerged plants in general, have been proven to interfere with fishing operations, causing loss of revenue (Dutta and Gupta, 1976). In New Zealand a number of submerged aquatic weeds including E. canadensis cause losses of up to 60,000 MW per hour each year as partial clog of screen intakes in hydropower stations (Howard-Williams, 1993).
Environmental ImpactTop of page
Elodea canadensis can from dense monospecific stands which can outcompete native plants for both space and nutrients and displace other aquatic plants from many localities, resulting in a decrease in biodiversity (NOBANIS, 2014). Dense stands reduce water movement, cut off light, produce anoxic conditions and trap sediments in the system (Simpson 1984; Barrat-Segretain, 2005). (Changes to invertebrate communities have also been reported (RAFTS, 2009). However, recent observations in Polish lakes showed no evidence that E. canadensis had any impact on the native flora or the ecological status of the lakes (Kolada and Kutyła, 2016).
Species of Elodea are also known to accumulate metals from the sediment and release them into the waterbody (RAFTS, 2009).
Social ImpactTop of page
Elodea canadensis can form large and dense stands that interfere with boating, fishing and thereby adversely affect recreation activities (McGavigan, 2017). It makes it difficult for boats to travel through invaded waterways (Bowmer et. al., 1995) reduces recreational opportunities and diminishes aesthetics for the environment (Josefsson and Andersson, 2001).
Risk and Impact FactorsTop of page
- Proved invasive outside its native range
- Is a habitat generalist
- Pioneering in disturbed areas
- Tolerant of shade
- Long lived
- Fast growing
- Has high reproductive potential
- Reproduces asexually
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Modification of hydrology
- Modification of natural benthic communities
- Modification of nutrient regime
- Modification of successional patterns
- Monoculture formation
- Negatively impacts cultural/traditional practices
- Negatively impacts livelihoods
- Negatively impacts aquaculture/fisheries
- Reduced native biodiversity
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Transportation disruption
- Competition - monopolizing resources
- Competition - shading
- Competition - smothering
- Competition - strangling
- Rapid growth
- Highly likely to be transported internationally accidentally
- Highly likely to be transported internationally deliberately
UsesTop of page
Although E. canadensis frequently occurs as a noxious weed, in warmer climates it is important to fish as a direct food source and for shade/shelter and as food for many birds, including ducks, coots, geese, grebes, swans, marsh birds, shore birds and game birds (Sculthorpe, 1971).
Uses ListTop of page
Animal feed, fodder, forage
- Fodder/animal feed
- Wildlife habitat
- Pet/aquarium trade
Similarities to Other Species/ConditionsTop of page
Identification of E. canadensis in its vegetative form can be confused with E. nuttallii and with another member of the Hydrocharitaceae family, Hydrilla verticillata, which both have similar habits within the USA.
Distinction between E. canadensis and E. nuttallii is possible from inflorescences: E. nuttallii has sessile male flowers, which are released at anthesis, and female flowers with a shorter floral tube (up to 9 cm). E. nuttallii can also occur as a common waterweed in the same geographic regions as it is rapidly expanding its distribution, but is not yet as widespread, though it is found in similar conditions and often seems to grow slightly more vigorously. The identification of both species is however sometimes confused and misidentifications occur. E. canadensis is characterized by a flat elongate leaf blade and a leaf length to width ratio of 3:1, whereas E. nuttallii has a ratio of 6:1 and typically has an obvious twist of at least half a turn along the length of the leaf blade. In some countries, the perceived occurrence of the two species of Elodea has been further confused because E. nuttallii, introduced to Britain in 1939, has displaced E. canadensis in many European waterways (Barrat-Segretain et al., 2002).
Distinction between E. canadensis and H. verticillata is easy after flowering, when H. verticillata forms short branchlets on the internodes and subterranean tubers on the rootstocks (Godfrey and Wooten, 1997). Holm et al. (1997) suggest that H. verticillata may be distinguished in the vegetative stage by its conspicuously toothed leaves, while confusion with Egeria densa is avoided by the fact that the latter has leaves in whorls of four or five, not three.
Prevention and ControlTop of page
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.
Early Warning Systems
The recent development of qPCR primers and probes for Elodea at the genus and species level offers the potential to detect the species during the early stages of invasion (Steinlage and Coleman, 2017).
Elodea canadensis is listed as a wild invasive non-native plant in Schedule 9 of the Wildlife and Countryside Act (England and Wales) and is included on the black list of certain European countries: Belgium (Branquart et al., 2010); Germany (Verbrugge et al., 2012).
In the US state of Alaska, any intentional movement of quarantined species, except for the purpose of identification, must be approved by the Division of Agriculture (11 AAC 34.145; 11 AAC 34.150) (Alaska Plant Materials Center, 2014).
Vehicles, boats, equipment and clothing should all be checked for fragments of the plant to prevent E. canadensis from being spread into new locations (RAFTS, 2009).
Draw-down control has been found to be effective for E. canadensis in experimental laboratory conditions (Barrat-Segretain and Cellot, 2007). The use of draw-down control is only possible in situations in which the water level can be managed. The drying out of lakes, ditches, ponds and irrigated fields is widely used, but is satisfactory only in countries with a prolonged dry season, or elsewhere in habitats which are easily drained (Surber, 1949; Clark, 1954; Walker, 1959). The technique has been moderately successful in the rice fields of tropical countries in eradicating E. canadensis and other submerged macrophytes. It is often supplemented by ploughing the dry soil with disks to a depth of about 25 cm.
Demonstrated effects include reducing direct sunlight by correctly-orientated marginal shade from vegetation or artificial materials near the water surface or also reducing the light penetration of water (Dawson, 1986). Reducing light intensity by shading is a good control method than could be applied to most submerged aquatic plants (Newman and Duenas, 2010). This has been observed in E. canadensis, which is adversely affected by shading (Larson, 2007b). This can be achieved by planting trees and by floating plastic covers, material or dyes to create shade (Newman and Duenas, 2010). An experimental study in the USA found that tree cover significantly reduced the total biomass of submerged macrophytes (Madsen and Adams, 1989); however, experimental results in the literature show that this could be counter-productive (Hussner et al., 2010). Films or sheets spread across lakebeds (benthic barriers) have also resulted in plant decomposition over a 3-week period, producing a weed-free environment, with no adverse environmental effects (Mayer, 1978).
Other environmental changes may include modification to the channel environment, manipulation of water flow through periodic or regular brief increases in water flow to wash out less stable vegetation or substrates, restructuring or reshaping channel shape, etc. (Dawson and Brabben, 1991; Bolton and Dawson, 1992). Restricting nutrient availability for example, the use of salt-rich water for secondary irrigation in Australia, is also likely to severely restrict the growth of freshwater plants. The use of lime has also been tested in order to reduce carbon availability for the plant but the effects were only short term (James, 2008).
Where submerged aquatic weeds cause blockage of penstock intake screens in New Zealand, the three methods commonly used for preventing such blockage are floating booms at an angle across the current to collect floating weed masses and concentrate them at a single site on the shore, mechanical screen cleaners on the intake screens, or lake draw-downs in summer to desiccate weed masses and in winter to freeze kill weed masses in shallow water (Howard-Williams, 1993).
In North America and Western Europe, special barges are used which cut the weeds and remove them from the water. Alternatively, cutting machines are mounted on boats or tractors. These are used in streams and small rivers letting the cut plant material float downstream (Westlake and Dawson, 1986). Mechanical mowing and rolling are widely practised in the control of weeds in irrigation ditches (Dunk and Tisdall, 1954; Seaman, 1958).) Cutting is best undertaken before July, when peak biomass is reached, preferably in March. This will provide approximately 8 to 10 weeks of control, and will delay the production of peak biomass (Newman and Duenas, 2010; McGavigan, 2017). Mechanical methods (cutting, draglines etc.) are not usually recommended as they break up the plant, allowing it to spread to new areas (Barrat-Segretain et al., 2002), but they can be useful in areas where the weed is already established or when the weed disperses into areas unfavourable to its survival (Bowmer et al., 1995).
Controlling aquatic weeds with herbicides has progressed most in the USA, Western Europe, Australia and New Zealand. A datasheet on control for the UK is available (Newman, 2005). In tropical countries, the use of herbicides is far more limited. For submerged plants, a number of chemicals were used but many are now prohibited in the USA (IARC, 2014) and elsewhere. Bensulfuron methyl has given fair control of E. canadensis in Australian irrigation channels (McCorkelle et al., 1990). An overview of chemical control methods published by the US Army Corps of Engineers, Waterways Experiment Station, lists dichlobenil, diquat alone and diquat with complexed copper as 'excellent' methods; and acrolein, Endothall [endothal] demethylalkylamine salts and fluridone as 'good' methods (Westerdahl and Getsinger, 1988).
Glomski et al. (2005) established that diquat gives excellent control of E. canadensis, even at low concentrations. Diquat is often used as the herbicidal component of gels that carry the herbicide into direct contact with the weed (Barratt, 1978; Chandrasena et al., 2012).
Elodea canadensis is susceptible to dichlobenil herbicide applied in spring before the plant is fully grown. However, sites treated with chemical control have experienced a regrowth of the plant between 2 and 3 years after treatment (McGavigan, 2017). The herbicide iofensulfuron‐sodium has also been found to reduce the shoot length by up to 45% (Wieczorek et al., 2017).
Control by aquatic herbivores has been investigated in numerous countries (National Academy of Sciences, 1976). Species tested include Tilapia melanopleura, T. mossambica and the Chinese grass carp Ctenopharyngodon idella. Since the latter is an exotic species, introduction is only allowed when the species can be confined to a particular waterbody and, therefore, investment in fences is a prerequisite. Nevertheless, several successful examples of control are known from Western Europe and the USA (Stott et al. 1971; Willey et al., 1974; Mitzner, 1978; Fowler, 1984) and more recent experiments have found medium efficiency in the use of stocking grass carps (Bonar et al., 2002, Pípalová, 2006). There are some disadvantages in using grass carp, as these fish are generalist feeders and may also damage native plant species (see Vernon and Hamilton, 2011 for further information).
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OrganizationsTop of page
Netherlands: European Weed Research Society - EWRS, Postbus 29, NL-6865 ZG Doorwerth, http://www.ewrs.org
UK: Centre for Ecology and Hydrology - CEH, CEH Wallingford, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire, http://www.ceh.ac.uk/
UK: Environment Agency, National Customer Contact Centre PO Box 544, Rotherham S60 1BY, http://www.environment-agency.gov.uk/
ContributorsTop of page
08/05/2018 Updated by:
Manuel Angel Duenas-Lopez, Universidad de Cordoba, Cordoba, Spain
02/10/2014 Updated by:
Ian Popay, Landcare Research, New Zealand
14/01/2008 Updated by:
Hugh Dawson, CEH Wallingford, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BB, UK
Distribution MapsTop of page
Select a dataset
CABI Summary Records
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