Myriophyllum heterophyllum
(broadleaf watermilfoil)

Pictures

Identity

Preferred Scientific Name

• Myriophyllum heterophyllum Michaux, 1803

Preferred Common Name

• broadleaf watermilfoil

International Common Names

• English: American water-milfoil; variable watermilfoil

Local Common Names

• Germany: Verschiedenblaettriges Tausendblatt
• Netherlands: Ongelijkbladig vederkruid
• USA: variable-leaf water milfoil

EPPO code

• MYPHE (Myriophyllum heterophyllum)

Summary of Invasiveness

M. 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.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Haloragidales
•                         Family: Haloragidaceae
•                             Genus: Myriophyllum
•                                 Species: Myriophyllum heterophyllum

Notes on Taxonomy and Nomenclature

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’.

Description

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).

Plant Type

Distribution

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).

Distribution Table

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.

History of Introduction and Spread

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.

Introductions

Risk of Introduction

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.'

Habitat

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.

Habitat List

Biology and Ecology

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/Altitude Ranges

Means of Movement and Dispersal

Pathway Causes

Pathway Vectors

Impact Summary

Economic Impact

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.

Environmental Impact

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).

Social Impact

M. heterophyllum forms dense stands in water bodies, which have negative effects on boating, swimming and aesthetics.

Risk and Impact Factors

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Highly mobile locally
• Fast growing
• Has high reproductive potential
• Reproduces asexually
• Has high genetic variability

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Monoculture formation
• Negatively impacts animal health
• Negatively impacts livelihoods
• Negatively impacts aquaculture/fisheries
• Negatively impacts tourism
• Reduced amenity values
• Transportation disruption
• Negatively impacts animal/plant collections

• Competition - monopolizing resources
• Competition - shading
• Hybridization
• Rapid growth
• Rooting

• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field
• Difficult/costly to control

Uses List

Environmental

• Wildlife habitat

General

• Pet/aquarium trade

Detection and Inspection

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).

Similarities to Other Species/Conditions

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.

Prevention and Control

References

Aiken SG, 1981. A conspectus of Myriophyllum (Haloragaceae) in North America. Brittonia, 33:57-69.

Cirujano S; Medina L; Stübing G; Peris JB, 1997. Myriophyllum heterophyllum Michx. (Haloragaceae), naturalized in Spain. Anales del Jardín Botánico de Madrid, 55(1):164-165.

DAISIE, 2009. Delivering Alien Invasive Species Inventories for Europe. http://www.europe-aliens.org

EPPO, 2007. EPPO reporting service no. 2007/085. EPPO reporting service no. 2007/085. Paris, France: European and Mediterranean Plant Protection Organization, unpaginated. http://archives.eppo.org/EPPOReporting/2007/Rse-0704.pdf

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/

Gerber D; Les D, 1996. Habitat differences among seven species of Myriophyllum (Haloragacea) in Wisconsin and Michigan. Michigan Botanist, 35:75-86.

Halstead JM; Michaud J; Hallas-Burt S; Gibbs JP, 2003. Hedonic analysis of effects of a nonnative invader (Myriophyllum heterophyllum) on New Hampshire (USA) lakefront properties. Environmental Management, 32(3):391-398.

Hussner A, 2005. Distribution of alien aquatic plants in the river Erft (North Rhine-Westphalia). (Zur Verbreitung aquatischer Neophyten in der Erft, Nordrhein-Westfalen.) Frankfurter Geobotanische Kolloquie, 19:55-58.

Kay SH; Hoyle ST, 2001. Mail order, the internet, and invasive aquatic weed. Journal Aquatic Plant Management, 39:88-91.

Lebreton A, 2013. Myriophyllum heterophyllum Michaux [Haloragaceae] in Haute-Vienne (Limousin, France), and the situation of this invasive plant in France and in Europe. (Myriophyllum heterophyllum Michaux [Haloragaceae] en Haute-Vienne (Limousin, France), et situation de cette plante invasive en France et en Europe.) Bulletin OEPP/EPPO Bulletin, 43(1):180-192. http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2338

Les DH; Mehrhoff LJ, 1999. Introduction of nonindigenous aquatic vascular plants in Southern New England: a historical perspective. Biological Invasions, 1(2/3):281-300. http://www.springerlink.com/(yqxryu55evlqoi4524ps0d45)/app/home/contribution.asp?referrer=parent&backto=issue,18,19;journal,25,26;linkingpublicationresults,1:103794,1

Moody ML; Les DH, 2002. Evidence of hybridity in invasive watermilfoil (Myriophyllum) populations. Proceedings of the National Academy of Sciences of the United States of America, 99(23):14867-14871.

Moody ML; Les DH, 2010. Systematics of the aquatic angiosperm genus Myriophyllum (Haloragaceae). Systematic Botany, 35:1-19.

Moody ML; Les DH; Ditomaso JM, 2008. The role of plant systematics in invasive aquatic plant management. Journal of Aquatic Plant Management, 46:7-15.

Pimentel D; Lach L; Zuniga R; Morrison D, 2000. Environmental and economic costs of nonindigenous species in the United States. BioScience, 50(1):53-65.

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.

Thum RA; Lennon JT, 2010. Comparative ecological niche models predict the invasive spread of variable-leaf milfoil (Myriophyllumheterophyllum) and its potential impact on closely related native species. Biological Invasions, 12(1):133-143. http://www.springerlink.com/content/x065475764481jnh/?p=b8eb71c07ab345d1a474d1e523242c58&pi=12

Thum RA; Lennon JT; Connor J; Smagula AP, 2006. A DNA fingerprinting approach for distinguishing native and non-native milfoils. Lake and Reservoir Management, 22:1-6.

USDA-NRCS, 2008. The PLANTS Database. Baton Rouge, USA: National Plant Data Center. http://plants.usda.gov/

Washington State Noxious Weed Control Board, 2007. Washington State noxious weed list. Washington State noxious weed list. unpaginated. http://www.nwcb.wa.gov

Yu Dan; Wang Dong; Li ZhenYu; Funston AM; 2002, publ. 2003. Taxonomic revision of the genus Myriophyllum (Haloragaceae) in China. Rhodora, 104(920):396-421.

Links to Websites

Organizations

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

Contributors

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

Distribution Maps