Eurasian watermilfoil Myriophyllum spicatum L. - Alaska Natural ...

Eurasian watermilfoil 

Myriophyllum spicatum L. 

Synonyms: None 

Other common names: myriophylle en epi, spike watermilfoil, spiked watermilfoil 

Family: Haloragaceae 

Invasiveness Rank: 90 The invasiveness rank is calculated based on a species’ ecological impacts, biological 

attributes, distribution, and response to control measures. The ranks are scaled from 0 to 100, with 0 representing a 

plant that poses no threat to native ecosystems and 100 representing a plant that poses a major threat to native 

ecosystems. 

Description 

Eurasian watermilfoil is a submersed, aquatic plant. 

Stems grow 91 cm long or longer. Leaves are whorled 

in groups of five, highly dissected, and composed of 28 

to 48 thread-like divisions. Spikes emerge above the 

water; flowers are borne in the axis of bracts. Fruits are 

2 to 3 mm long (Royer and Dickinson 1999, DiTomaso 

and Healy 2003). 

Myriophyllum spicatum L. Photo by A. Fox. 

Similar species: Northern watermilfoil (M. sibiricum 

Fern.) is often mistaken for Eurasian watermilfoil, but it 

can be distinguished from Eurasian watermilfoil by its 

leaves. Northern watermilfoil leaves have only 12 to 24 

thread-like segments, whereas Eurasian watermilfoil 

leaves have 28 to 48 thread-like segments (Royer and 

Dickinson 1999). Eurasian watermilfoil can also be 

confused with the native whorl-leaf watermilfoil, M. 

verticillatum. Unlike Eurasian watermilfoil, whorl-leaf 

watermilfoil has four, rather than five, leaves per whorl 

and its leaves exceed the length of its internodes. 

Ecological Impact 

Impact on community composition, structure, and 

interactions: Eurasian watermilfoil forms dense 

canopies that often shade out or displace native 

vegetation and reduce natural diversity. Monospecific 

stands of Eurasian watermilfoil offer poor habitats for 

waterfowl, fish, and other wildlife. The reduction in 

water flow caused by stands of Eurasian watermilfoil 

creates good breeding grounds for mosquitoes 

(DiTomaso and Healy 2003, Jacono and Richerson 

2004). 

Impact on ecosystem processes: Dense mats of Eurasian 

watermilfoil can increase sedimentation by slowing 

water flow, allowing suspended sediment to settle. They 

also alter water quality by increasing temperature and 

pH and decreasing dissolved oxygen beneath the mats. 

Biology and Invasive Potential 

Reproductive potential: Eurasian watermilfoil 

reproduces by seeds, fragmentation, and winter buds. 

Young populations of Eurasian watermilfoil average 

112 seeds per stalk. Despite high seed production, 

fragmentation and winter buds probably contribute more 

to the reproduction of this species than does the 

germination of seeds. Winter buds are tight leaf clusters 

borne near the ends of stems. They develop when water 

temperatures drop and length of daylight shortens. The 

buds break off of the stems and sink to the bottom of the 

water, where they overwinter. In spring, the buds grow 

and elongate to form new plants (Washington State 

Department of Ecology 2003). 

Role of disturbance in establishment: Eurasian 

watermilfoil thrives in areas that have been subjected to 

various kinds of natural and anthropogenic disturbances. 

Potential for long-distance dispersal: Fragments and 

winter buds may be transported long distances by 

flowing water. 

Potential to be spread by human activity: This species 

can be spread from lake to lake on boat trailers. 

Germination requirements: Unknown. 

Growth requirements: Eurasian watermilfoil is an 

Last Updated: 2011-02-08 by Helen Klein 

http://aknhp.uaa.alaska.edu

extremely adaptable plant; it is able to tolerate and 

thrive in a wide variety of environmental conditions. It 

grows in still to moderately flowing waters, roots in 

water depths from 1 to 10 meters, and can survive under 

ice. It can tolerate pH from 5.4 to 11 and a broad range 

of temperatures. Eurasian watermilfoil requires large 

amounts of light. It grows best on fine-textured, 

inorganic sediments, whereas it grows relatively poorly 

on highly organic sediments (Jacono and Richerson 

2004). 

Congeneric weeds: Parrot feather watermilfoil 

(Myriophyllum aquaticum) is considered a noxious 

weed in Alabama, Maine, New Hampshire, Vermont, 

and Washington (Invaders 2010, USDA 2010). 

Legal Listings 

Has not been declared noxious 

Listed noxious in Alaska 

Listed noxious by other states (AL, CO, CT, FL, ID, 

MA, ME, MT, NC, NM, NV, OR, SC, SD, TX, VT, 

WA) 

Federal noxious weed 

Listed noxious in Canada or other countries (AB) 

Distribution and abundance 

Typical habitat for Eurasian watermilfoil includes fresh 

to brackish water in fish ponds, lakes, slow-moving 

streams, reservoirs, estuaries, and canals. 

Native and current distribution: Eurasian watermilfoil is 

native to Europe, Asia, and northern Africa. It now 

grows in North America, South America, Australia, 

Greenland, Central Africa, and South Africa. It has been 

found in 43 states of the United States and in the 

Canadian provinces of British Columbia, Ontario, and 

Quebec (Jacono and Richerson 2004). This species has 

not been documented in Alaska. 

Management 

Once Eurasian watermilfoil becomes well established 

within a body of water, it is very difficult or impossible 

to remove. In small bodies of water, there have been 

some cases of limited success in controlling infestations 

using aquatic herbicides. Other control methods include 

harvesting, rotovation, installation of bottom barriers, 

and hand pulling by divers. 

References: 

DiTomaso, J.M. and E.A. Healy. 2003. Aquatic and 

riparian weeds of the West. California: 

University of California, Agriculture and 

Natural Resources; pp. 86-95. 

Invaders Database System. 2010. University of 

Montana. Missoula, MT. 

http://invader.dbs.umt.edu/ 

Jacono, C.C. and M.M. Richerson. 2004. 

Nonindigenous Aquatic Plants. Myriophyllum 

spicatum L. U.S. Department of the Interior. 

Geological Survey. Biological Resources 

Division. Center for Aquatic Resource Studies. 

http://nas.er.usgs.gov 

Royer, F. and R. Dickinson. 1999. Weeds of the 

Northern U.S. and Canada. The University of 

Alberta press. 434 pp. 

USDA. 2010. The PLANTS Database. National Plant 

Data Center, Natural Resources Conservation 

Service, United States Department of 

Agriculture. Baton Rouge, LA. 

http://plants.usda.gov 

Washington State Department of Ecology: Water 

Quality Home. 2003. Non-Native Freshwater 

Plants. Eurasian Watermilfoil. 

http://www.ecy.wa.gov/programs/wq/plants/we 

eds 

Last Updated: 2011-02-08 by Helen Klein 

http://aknhp.uaa.alaska.edu

Eurasian watermilfoil Myriophyllum spicatum L. - Alaska Natural ...

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