Dear Friends of Maine Lakes, Thank you for visiting our Interactive Field Guide! Though the primary content pertaining to species identification in this Guide is—for the most part—still correct and useful, the site itself is no longer fully-functional (nor able to be updated). The entire Guide will soon be replaced by a new, expanded website-version of the Maine Field Guide to Aquatic Phenomena. So please stay tuned! Thank you for your patience!

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Milfoil comparison table
Milfoil comparison table

Myriophyllum spicatum

NOTE: All leafy milfoils display a wide range of
vegetative variability. Any milfoil found in Maine waters should be considered suspicious until a positive identification has been confirmed by someone with the appropriate expertise.

Eurasian Milfoil colony
Eurasian water-milfoil in-situ

Habitat: Eurasian water-milfoil is an extremely well adapted plant, able to thrive in a wide variety of environmental conditions. It grows well in still and flowing waters, tolerates mild salinites and can survive under ice. Eurasian water-milfoil grows rooted in water depths from 1 to 10 meters, generally reaching the surface in depths of 3 to 5 meters. Though adapted to a wide variety of substrate types, this species seems to favor fine-textured, inorganic sediments.

Eurasian Milfoil Whorl
Whorl of leaves; typically greater than
twelve leaflet pairs per leaf

Description: Branching stems of Eurasian water-milfoil emerge from dense, spreading roots. The leaves are arranged in whorls of 3 to 6 leaves (4 leaves per whorl is common). The whorls are openly spaced along the stem, with 1 to 3 cm between nodes. The leaves are finely feather-divided, typically with 12 to 24 pairs of thread-like leaflets on each leaf. Since the leaves of other milfoil species generally have fewer than 14 leaflet pairs, counting leaflets can provide helpful clues to identifying Eurasian water-milfoil. (Note that the occasional Eurasian milfoil leaf may have as few as 5 leaflet pairs. For this reason it is always advised to count leaflet pairs on several leaves, taken from various points along the stem.) The tips of the leaves often have a blunt, snipped-off appearance. Flowers and bracts occur in whorls on slender flower spikes that rise above the water surface. The bracts have smooth margins and the flowers are generally larger than the bracts. Eurasian water-milfoil does not form winter buds.

Eurasian Milfoil Range Map
U.S. range map of Eurasian water-milfol

Origin and U.S. Range: Eurasian water-milfoil is native to Europe and Asia. It was introduced to North America in the 1940s. Spreading rapidly since its introduction, Eurasian water-milfoil is now present in most states, including Maine. It also occurs in most Canadian provinces including Quebec.

Eurasian Milfoil Flower
Flowers and bracts are arranged in
whorls on the emergent flower spike;
the flowers are larger than the bracts

Annual Cycle: Eurasian water-milfoil is an extremely hardy aquatic perennial that propagates through root division, fragmentation, and seeds. Flowering spikes typically emerge from the water in mid to late summer, but not all colonies produce flowers. Auto-fragmentation may occur during the growing season with stem sections developing roots even before they separate from the parent plant. Toward the end of the growing season some plants break apart and die back to their rootstalks; others overwinter intact. New growth sprouts from roots and overwintering plants and plant fragments as the water begins to warm in the spring, growing rapidly toward the surface. Certain milfoils are able to hybridize with other, closely related, milfoil species. Eurasian water-milfoil is known to hybridize with Maines native northern water-milfoil.

Look Alikes: May be confused with bladderworts, hornworts, mermaid weeds, water crowfoots, and other leafy water-milfoils.

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Eurasian Water Milfoil flower Eurasian Water Milfoil specimen Eurasian Water Milfoil stem Eurasian Water Milfoil whorl Eurasian Water Milfoil range map Eurasian Water Milfoil Illustration

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