Eurasian Water Milfoil
Habitat: Eurasian water-milfoil is found in the submersed plant community. It is an extremely well adapted plant and is able to thrive in a wide variety of environmental conditions. It grows well in still and flowing waters, it tolerates mild salinities, and can survive under ice. Eurasian water-milfoil grows rooted in water depths from 1-10 metres, generally reaching the surface in depths of 3-5 metres. Though adapted to a wide variety of substrate types, this species seems to favour fine-textured, inorganic sediments.
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 threadlike leaflets on each leaf. 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.
Origin and Range: This aquatic plant is native to Europe and Asia. It was introduced to North America in the 1940s. Spreading rapidly since introduction, Eurasian water-milfoil is now present in most states and Canadian provinces. In Canada, the species is known to occur in New Brunswick, Quebec, Ontario, Manitoba, and British Columbia.
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. Towards the end of the growing season some plants break apart and die back to their root stalks; 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.
Look Alikes: Eurasian water-milfoil may be confused with other native milfoils. Since the leaves of other similar milfoil species generally have fewer than 14 leaflet pairs, counting leaflets can provide helpful clues in identifying Eurasian water-milfoil. NOTE: The occasional Eurasian water-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.
Impacts: Eurasian water-milfoil forms thick mats that can interfere with swim¬ming, fishing, waterfowl hunting, and boating because
plant fragments become wrapped around propellers. Fish and wildlife are also impacted because nutrient-rich native plants are displaced, and the economy is impacted as these infestations reduce local property values.