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Generate reportM. heterophyllum is an aquatic plant native to southeast USA. It is considered invasive throughout New England and northwest USA and as an emerging invader in Europe because of its tendency for uncontrolled growth and subsequent formation of dense mats of submergent vegetative material throughout the water column and at the water surface. These mats prevent water flow, reduce sunlight, reduce oxygen availability, and impede swimming, boating and fishing. M. heterophyllum is banned from sale in some New England states and Washington state.
Common names include variable-leaf watermilfoil, two-leaf watermilfoil and broad-leaf watermilfoil. The exact origins of these names are not known, but are presumed to be North American. In the aquarium trade, M. heterophyllum may be sold as ‘myrio’, ‘foxtail’, or ‘parrotfeather’.
M. heterophyllum is an aquatic plant that has submerged vegetation with emergent flowering spikes. Plants hermaphroditic, occasionally monoecious. Stem stout, to 100 cm; internodes crowded. Submerged leaves 4- or 5-whorled or scattered, pectinate, oblong in outline, (1.5-)2-4 × 1-3 cm; segments in 5-12 pairs, filiform, 0.5-1.5 cm. Inflorescence a terminal spike of 4-whorled flowers, 5-35 cm, in monoecious plants lowermost flowers female, uppermost ones male; bracts persistent, eventually reflexed, lanceolate to oblong or obovate, 4-18 × 1-3 mm, margin sharply serrulate; bracteoles ovate, ca. 1.2 × 0.6 mm, margin serrate. Petals 1.5-3 mm. Stamens 4. Fruit 4-loculed, subglobose, 1-1.5 mm; mericarps with 2 finely tuberculate ridges abaxially, apex beaked (Flora of China Editorial Committee, 2012).
The distribution of M. heterophyllum is generally known, but not documented in detail. Aiken (1981) lists its distribution in North America as ‘…Virginia to Florida, northward to Ontario and Michigan, and westward to Missouri and Texas’. The species is generally considered as native to the eastern part of the USA, except the northeastern region. It is considered non-native and invasive in New England, where it appears to have been introduced circa 1932 via escape from cultivation with subsequent spread via vegetative propagules (Les and Mehrhoff, 1999). Since its initial introduction to New England, it has spread throughout the region and is the most common invasive aquatic plant in New Hampshire (Thum and Lennon, 2009). It is not clear if M. heterophyllum was historically native to the mid-Atlantic region (Delaware, Maryland, New Jersey, New York, Pennsylvania and Virginia). For example, it is treated as a non-native invasive species in New York and eastern Pennsylvania, but is considered an extremely rare native and threatened species in nearby Delaware. Part of the confusion regarding its historical status (native/non-native) in northeastern USA may result from confusion with the closely related species M. pinnatum, which is considered native along the eastern coast from Florida through eastern Massachussetts (Aiken, 1981). M. heterophyllum is also considered non-native in western USA: while it is not clear when it was first introduced here, its recent spread in the region - especially in Washington state - is causing concern among water resource managers. Two causes for concern include the possible misidentification of M. heterophyllum with the closely-related, morphologically similar, and endemic western watermilfoil, M. hippuroides, and the potential for hybridization between the two species.
In Europe, it is found in Austria, Belgium, France, Germany, Netherlands and Spain (EPPO, 2012, 2014).
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 |
|---|---|---|---|---|---|---|---|
Asia |
|||||||
| China | Present | Introduced | Original citation: Yu et al. (2002, publ. 2003) | ||||
| -Guangdong | Present | Introduced | |||||
Europe |
|||||||
| Austria | Present | Introduced | First reported: <1885 | ||||
| Belgium | Present | Introduced | 1984 | ||||
| Croatia | Present, Few occurrences | ||||||
| France | Present, Few occurrences | ||||||
| Germany | Present, Localized | Introduced | Invasive | First recorded in North Rhine-Westphalia in 1979. Found in eastern Germany since 1960 spreading west | |||
| Greece | Absent, Invalid presence record(s) | ||||||
| Netherlands | Present | Introduced | Invasive | ||||
| Spain | Present | Introduced | |||||
| Sweden | Absent | ||||||
| Switzerland | Present | ||||||
| United Kingdom | Absent, Eradicated | ||||||
North America |
|||||||
| Canada | Present | ||||||
| -Alberta | Present | ||||||
| -British Columbia | Present | Potential for confusion with native M. hippuroides | |||||
| -New Brunswick | Present | ||||||
| -Ontario | Present | Native | |||||
| -Quebec | Present | ||||||
| Guatemala | Present | ||||||
| Mexico | Present | ||||||
| United States | Present | ||||||
| -Alabama | Present | Native | |||||
| -Arkansas | Present | Native | |||||
| -Connecticut | Present, Few occurrences | Introduced | 1932 | Invasive | |||
| -Delaware | Present, Few occurrences | Native | Considered native but very rare. Confusion with other species may complicate account of species here | ||||
| -Florida | Present, Widespread | Native | Widespread throughout state, but not necessarily abundant | ||||
| -Georgia | Present | Native | Known from locations throughout the state, but not necessarily abundant throughout | ||||
| -Illinois | Present | ||||||
| -Indiana | Present | Occurs commonly in northern portion of state | |||||
| -Iowa | Present | ||||||
| -Kansas | Present | ||||||
| -Kentucky | Present | Very rare species of special concern | |||||
| -Louisiana | Present, Widespread | ||||||
| -Maine | Present, Few occurrences | Invasive | |||||
| -Maryland | Present | ||||||
| -Massachusetts | Present | Invasive | Prohibited plant in this state | ||||
| -Michigan | Present, Widespread | Native | |||||
| -Minnesota | Present, Localized | ||||||
| -Mississippi | Present | ||||||
| -Missouri | Present | Native | |||||
| -New Hampshire | Present, Widespread | Introduced | Invasive | ||||
| -New Jersey | Present | Historical status of species uncertain and may be complicated by confusion with closely-related milfoils, especially M. pinnatum | |||||
| -New Mexico | Present | ||||||
| -New York | Present | Historical status of species uncertain and may be complicated by confusion with closely-related milfoils, especially M. pinnatum | |||||
| -North Carolina | Present | Native | Occurs along the eastern portion of the state | ||||
| -North Dakota | Present | ||||||
| -Ohio | Present, Few occurrences | Native | Considered endangered | ||||
| -Oklahoma | Present, Localized | Native | Found in southeastern portion of state | ||||
| -Oregon | Present | ||||||
| -Pennsylvania | Present | Considered native and endangered to western portion of state. Considered non-native and invasive in eastern portion of state | |||||
| -Rhode Island | Present | ||||||
| -South Carolina | Present, Widespread | Native | Common in eastern portions of the state | ||||
| -South Dakota | Present | ||||||
| -Tennessee | Present | Native | |||||
| -Texas | Present | ||||||
| -Vermont | Present, Localized | Introduced | Discovered in 2008 in a single location, possibly eradicated after discovery | ||||
| -Virginia | Present | Native | |||||
| -Washington | Present, Few occurrences | Invasive | |||||
| -West Virginia | Present | ||||||
| -Wisconsin | Present | Native | |||||
Although native to eastern North America, M. heterophyllum is not considered native to northeastern USA. The first recorded observation of the species in northeastern USA was from Bridgeport, CT in 1932. Les and Mehrhoff (1999) presume the original introduction can be attributed to escape from cultivation, with subsequent spread by vegetative propagules escaping cultivation. Recent genetic analyses suggest that M. heterophyllum may have been independently introduced to northeastern USA on several occasions (R Thum, Grand Valley State University, USA, personal communication, 2010).
Very little is known about the history of introduction to western USA. The Washington State Noxious Weed Control Board (2007) claims that only four populations of M. heterophyllum have been found in the state, all within private lakes, while the Aquatic Plant Monitoring project at the University of Washington has 5 locations listed throughout the state of Washington as having M. heterophyllum (see http://www.ecy.wa.gov/programs/eap/lakes/aquaticplants/).
In Europe, M. heterophyllum was first recorded in Germany in the 1960s, but details regarding its introduction and spread are lacking (Hussner, 2005). The species is also reportedly naturalized in Spain (Cirujano et al., 1997). It was first reported from France, in a private pond in Haute-Vienne department, in 2011 (Lebreton, 2013).
M. heterophyllum has also been reported in China (Yu et al., 2002), but details regarding its history and spread are lacking.
| Introduced to | Introduced from | Year | Reason | Introduced by | Established in wild through | References | Notes | |
|---|---|---|---|---|---|---|---|---|
| Natural reproduction | Continuous restocking | |||||||
| China | Yu et al. (2002, publ. 2003) | Possibly from USA | ||||||
| Connecticut | USA | 1932 | Escape from confinement or garden escape (pathway cause) | Yes | Les and Mehrhoff (1999) | Has spread throughout northeastern USA | ||
| Germany | Circa 1960s | Yes | Hussner (2005) | Possibly from USA | ||||
| Spain | Yes | Cirujano et al. (1997) | Possibly from USA | |||||
| Washington | USA | Washington State Noxious Weed Control Board (2007) | ||||||
M. heterophyllum is a popular plant in the aquarium and water gardening trades and can readily be obtained from any number of aquatic plant vendors under a variety of names. Plants genetically confirmed as M. heterophyllum have been purchased from a variety of vendors under a variety of common names (myrio, foxtail, and parrotfeather) and scientific names of (M. heterophyllum, M. pinnatum, M. tuberculum, M. aquaticum and M. simulans). Once escaped from an aquarium or cultivated pond, M. heterophyllum is capable of spreading through vegetative fragments. As such, it can be moved around by any number of water and animal vectors and may be commonly transported among water bodies on boats and boat trailers. Seeds may also be dispersed by animal vectors.
EPPO (2012) considers M. heterophyllum to have the potential to become invasive across Europe, 'especially in shallow lakes and channels.'
Gerber and Les (1996) found M. heterophyllum to be associated with water bodies that had higher pH and calcium levels relative to other species of milfoils in Michigan and Wisconsin. Thum and Lennon (2010) found M. heterophyllum to be associated with higher order lakes - large, low elevation lakes with relatively high pH, alkalinity and conductivity - in its introduced range in New Hampshire, USA. However, it is not clear whether these relationships hold true across different geographic areas where the species occurs, or among distinct genetic lineages of M. heterophyllum.
| Category | Sub-Category | Habitat | Presence | Status |
|---|---|---|---|---|
| Littoral | Coastal areas | Present, no further details | Harmful (pest or invasive) | |
| Littoral | Coastal areas | Present, no further details | Natural | |
| Littoral | Mud flats | Present, no further details | Harmful (pest or invasive) | |
| Littoral | Mud flats | Present, no further details | Natural | |
| Freshwater | ||||
| Freshwater | Irrigation channels | Present, no further details | Harmful (pest or invasive) | |
| Freshwater | Irrigation channels | Present, no further details | Natural | |
| Freshwater | Lakes | Principal habitat | Harmful (pest or invasive) | |
| Freshwater | Lakes | Principal habitat | Natural | |
| Freshwater | Reservoirs | Principal habitat | Harmful (pest or invasive) | |
| Freshwater | Reservoirs | Principal habitat | Natural | |
| Freshwater | Rivers / streams | Principal habitat | Harmful (pest or invasive) | |
| Freshwater | Rivers / streams | Principal habitat | Natural | |
| Freshwater | Ponds | Principal habitat | Harmful (pest or invasive) | |
| Freshwater | Ponds | Principal habitat | Natural |
Reproduction may occur through asexual vegetative propagation and also sexual reproduction (seed production). Asexual vegetative propagation is thought to be the dominant mode of reproduction in introduced populations (e.g. Washington State Noxious Weed Control Board factsheet) (http://www.nwcb.wa.gov/). The emergent flowers are wind-pollinated.
| Latitude North (°N) | Latitude South (°S) | Altitude Lower (m) | Altitude Upper (m) |
|---|---|---|---|
| 50 | 25 |
| Cause | Notes | Long Distance | Local | References |
|---|---|---|---|---|
| Hitchhiker | May attach to boats and boat trailers | Yes | ||
| Internet sales | Yes | Yes | Kay and Hoyle (2001); Moody et al. (2008) | |
| Pet trade | Yes | Yes | Kay and Hoyle (2001); Moody et al. (2008) |
| Vector | Notes | Long Distance | Local | References |
|---|---|---|---|---|
| Floating vegetation and debris | Vegetative fragments can re-root | Yes | ||
| Internet sales | Yes | Yes | ||
| Pets and aquarium species | Yes | Yes | ||
| Ship hull fouling | Yes | |||
| Ship structures above the water line | Yes | |||
| Water | Yes |
| Category | Impact |
|---|---|
| Economic/livelihood | Positive and negative |
| Environment (generally) | Positive and negative |
In general, aquatic invasive weeds in the USA cost about $110 million annually (Pimentel et al., 2000). In the specific case of M. heterophyllum, it has been associated with up to a 40% decrease in property values in New Hampshire (Halstead et al., 2003) in addition to costs associated with control.
M. heterophyllum is highly competitive and able to outcompete other aquatic plants. It forms dense mats of submergent vegetative material throughout the water column and at the water surface, which can prevent water flow, reduce sunlight and reduce oxygen availability. The resulting low oxygen conditions can harm or kill aquatic organisms (EPPO, 2012).
M. heterophyllum forms dense stands in water bodies, which have negative effects on boating, swimming and aesthetics.
Morphological keys (such as Aiken, 1981) are available but rely mostly on characters of flowers and fruits, which may not be present, as M. heterophyllum rarely flowers. It can best be recognised by its dense underwater growth and undivided, serrate emergent leaves (Q-bank, 2015).
Genetic identifications using the nuclear ribosomal DNA internal transcribed spacer regions (ITS) have become common (Moody and Les, 2002; Thum et al., 2006).
M. heterophyllum may be confused with any number of Myriophyllum species. In general, Myriophyllum are distinguished by characters of flowers and fruits, which may not be present. Vegetative material of M. heterophyllum may especially be confused with closely related species M. humile, M. farwelli, M. pinnatum, M. laxum, and M. hippuroides. However, misidentifications with more distantly related species also occur (Aiken, 1981; Thum et al., 2006), especially M. verticillatum.
Genetic identifications using the nuclear ribosomal DNA internal transcribed spacer regions (ITS) have become common (Moody and Les, 2002; Thum et al., 2006). However, further work on the reliability of these markers based on much larger sample sizes is needed.
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.
Aiken SG, 1981. A conspectus of Myriophyllum (Haloragaceae) in North America. Brittonia, 33:57-69.
DAISIE, 2009. Delivering Alien Invasive Species Inventories for Europe. http://www.europe-aliens.org
EPPO, 2011. EPPO Reporting Service. EPPO Reporting Service. Paris, France: EPPO. http://archives.eppo.org/EPPOReporting/Reporting_Archives.htm
EPPO, 2012. Myriophyllum heterophyllum (Haloragaceae). Invasive Alien Plants. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/INVASIVE_PLANTS/iap_list/Myriophyllum_heterophyllum.htm
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
Flora of China Editorial Committee, 2012. Flora of China Web. Cambridge, USA: Harvard University Herbaria. http://flora.huh.harvard.edu/china/
Q-bank, 2013. Comprehensive databases of quarantine plant pests and diseases. http://www.q-bank.eu/
Stace C, 1991. New Flora of the British Isles. Cambridge, UK: Cambridge University Press.
CABI, Undated. Compendium record. Wallingford, UK: CABI
CABI, Undated a. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI
Flora of China Editorial Committee, 2012. Flora of China Web., Cambridge, USA: Harvard University Herbaria. http://flora.huh.harvard.edu/china/
Q-bank, 2013. Comprehensive databases of quarantine plant pests and diseases., http://www.q-bank.eu/
Stace C, 1991. New Flora of the British Isles. Cambridge, UK: Cambridge University Press.
| Website | URL | Comment |
|---|---|---|
| Connecticut Invasive Plant Council | http://nbii-nin.ciesin.columbia.edu/ipane/ctcouncil/CT_Invasive_Plant_List.htm | |
| GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway | https://doi.org/10.5061/dryad.m93f6 | Data source for updated system data added to species habitat list. |
| Global register of Introduced and Invasive species (GRIIS) | http://griis.org/ | Data source for updated system data added to species habitat list. |
| Massachusetts Department of Agricultural Resources | http://www.mass.gov/agr/ | |
| Massachusetts Department of Conservation and Recreation | http://www.mass.gov/dcr/ | |
| University of Washington Aquatic Plant Monitoring Project | http://www.ecy.wa.gov/programs/eap/lakes/aquaticplants/ | |
| USDA-PLANTS | http://plants.usda.gov | |
| Vermont Department of Agriculture | http://www.vermontagriculture.com/ | |
| Washington State Noxious Weed Control Board (NWCB) | http://www.nwcb.wa.gov/ |
Europe: DAISIE - Delivering Alien Invasive Species Inventories for Europe, Web-based service, http://www.europe-aliens.org
France: European and Mediterranean Plant Protection Organisation (EPPO), OEPP/EPPO, 1 rue Le Notre, 75016 Paris, http://www.eppo.org/
USA: MVLMP (Maine Volunteer Lake Monitors), 24 Maple Hill Road, Auburn, ME 04210, http://www.mainevolunteerlakemonitors.org
01/06/09 Original text by:
Ryan Thum, Grand Valley State University Grand Valley State University, Annis Water Resources Institute, 224 Lake Michigan Center, 740 West Shoreline Drive, Muskegon, MI 49441, 616-331-3989, USA
Matthew Zuelig, Grand Valley State University, Annis Water Resources Institute, 224 Lake Michigan Center, 740 West Shoreline Drive, Muskegon, MI 49441, 616-331-3989, USA
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