Eurasian watermilfoil

Myriophyllum spicatum

Keys to Identification

Family

Water Milfoil (Halorgaceae)

USDA Code

MYSP2

Legal Status

Colorado List B Noxious Weed

Identification

Lifecycle

Submersed perennial

Growth form

Herb

Flower

Tiny pink, usually flower in mid to late July.

Seeds/Fruit

Many seeds produced, not a factor in reproduction.

Leaves

Leaves are divided into leaflets that are threadlike, usually in more than 14 pairs.

Stems

Long underwater stems that are branched which produce leaves near the surface of the water.

Roots

Plants die back to root crowns in fall, sprouting in spring.

Seedling

Rare, never observed occurring naturally.

Colonization

New colonies are usually a result of fragmentation. The plant can auto-fragment, producing roots before separation. Activities such as boating and natural processes such as wind and wave action can also cause fragmentation. Each fragment can become a new plant.

Similar Species

Natives

Native milfoil

Impacts

Agricultural

Dense mats clog waterways.

Ecological

Growth of the thick vegetative mats degrade water quality and reduce dissolved oxygen levels. Dense mats can restrict recreation and can foul beaches when the mats begin to decay.

Habitat and Distribution

General requirements

Lakes, ponds, shallow reservoirs and low energy areas of rivers and streams.

Distribution

Confirmed in 45 states and in Canada.

Historical

Native range was Europe, Asia, and northern Africa. First documented in the US in 1942, thought to have been intentionally introduced.

 

References

Couch, R., and E. Nelson. 1985. Myriophyllum spicatum in North America. Pp. 8-18 in L.W.J. Anderson (ed.). First International Symposium Watermilfoil and Related Haloragaceae Species. 23-24 July 1985, Vancouver , B.C. Aquatic Plant Management Society, Vicksburg, MS

Madsen, J.D., J.W. Sutherland, J.A. Bloomfield, L.W. Eichler, and C.W. Boylen. 1991. The decline of native vegetation under dense Eurasian watermilfoil canopies. J. Aquatic Plant Management 29:94-99.

Nichols, S. A. 1975. Identification and management of Eurasian Water Milfoil in Wisconsin. Wisconsin Academy of Sciences, Arts and Letters 63:116-126.

Nichols, S. A. 1994. Evaluation of invasions and declines of submersed macrophytes for the Upper Great Lakes Region. Lake and Reservoir Management 10(1):29-33.

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