Myriophyllum spicatum

Eurasian Water-milfoil

NOT NATIVE TO MAINE - INVASIVE

NOTE: All leafy milfoils display a wide range of vegetative variability. All milfoils found in Maine waters should be considered “suspect” as potential invaders until a positive identification has been confirmed.

Habitat: Eurasian water-milfoil is an extremely well adapted plant, able thrive in a wide variety of environmental conditions. It grows well in still and flowing waters, tolerates mild salinities 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. Adaptable to a wide variety of substrate types, this species seems to favor fine-textured, inorganic sediments. The plants grow rapidly, branching profusely at the surface where they form dense floating mats, choking and shading out all other plants in the area. Infestations render waters unsuitable for boating, swimming, fishing, and other recreational uses.

Description: Eurasian water-milfoil is a submersed aquatic plant with feather-like finely divided leaves, typically with 12 to 24 pairs of thread-like leaflets on each leaf. (Since the leaves of most other milfoil species generally have less than 14 leaflet pairs, counting leaflets can be helpful in distinguishing Eurasian watermilfoil from other milfoil species. Note that in some cases Eurasian water-milfoil leaves may have as few as 5 leaflet pairs. The greater number of leaves observed, the better the chance of making an accurate determination.) The leaves are arranged in whorls (3 to 6 leaves per whorl). The whorls are openly spaced along the stem, with 1 to 3 cm between whorls. Flowers occur in the axils of the bracts, arranged in whorls around a slender spike that emerges generally upright from the surface of the water. The bracts have smooth margins and the flowers are generally larger than the bracts. Eurasian water-milfoil does not form winter buds.

Origin and Range: Eurasian water-milfoil is native to Europe and Asia. It was introduced to North America in the 1940’s and is now considered to be one of the most problematic aquatic invaders in the United States. Spreading rapidly since its introduction, Eurasian water-milfoil has now been confirmed in most US states including Maine. It also occurs in most Canadian provinces including Quebec.

Annual Cycle: Eurasian water-milfoil is extremely hardy. It survives winter primarily as rootstalks, but whole plants and stem fragments may also over-winter. Flowering spikes may emerge from the water in mid to late summer, but not all colonies produce spikes. Like all leafy milfoils, this plant propagates easily from stem fragments. Some water-milfoils are known to hybridize with each other.

Look Alikes: May be confused with other water-milfoil species, water marigold, coontail, bladderwort, water crowfoot, fanwort, or mermaid weed.