VARIABLE WATER-MILFOIL
Myriophyllum heterophyllum
NOT NATIVE TO MAINE - INVASIVE
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.
variable water-milfoil in-situ
Habitat: Variable 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, and can survive under ice. Variable water-milfoil grows rooted in water depths from 1 to 5 meters on various substrates including organic muck, silt, sand and gravel. Plants stranded on dewatered shorelines form erect spikes known as “terrestrial morphs.” The morphs, resembling miniature pine trees, will remain in this land-adapted form until the waters return, at which time they will “morph” back into submersed aquatic plants.
Flowers and bracts are arranged in whorls
on the emergent flower spike; the blade-
shaped serrated bracts are larger than the
tiny white flowers that occur in their axils
Description: Variable water-milfoil is a submersed, aquatic plant with branching stems emerging from dense, spreading roots. Feather-divided leaves are arranged in densely packed whorls. (Leaves along lower portions of the stem may not be in perfect whorls, i.e., some leaves may be slightly offset.) There are generally 4 to 6 leaves per whorl and 5 to 14 pairs of thread-like leaflets on each leaf. The dense leaf arrangement gives this plant a bottle brush appearance. Stems may be green and slight, but most often they are thick, robust and reddish in color (even bright red). Flowers and bracts are arranged in whorls on an emergent flower spike. The tiny white flowers occur in the axils of the bracts. The bracts are blade-shaped, serrated, and more than twice the length of the flower. Winter buds (or turions) are formed in the fall at the base of the stems or on the rhizomes.
U.S. range map of variable water-milfoil
Origin and U.S. Range: Variable water-milfoil is native to parts of the United States, but not native to New England. Variable water-milfoil is present in Maine and all New England states except Vermont. A hybrid of this species (M. heterophyllum x M. laxum), has also been confirmed in Maine.
Whorls of submersed leaves are
densely arranged, giving plants a
"bottle brush" appearance
Annual Cycle: Variable water-milfoil is an extremely hardy aquatic perennial that propagates through root division, fragmentation, turions 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 turions, roots, 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.
Look Alikes: May be confused with bladderworts, hornworts, mermaid weeds, water crowfoots, and other leafy water-milfoils.
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 Water Quality Monitoring |  Aquatic Invasive Monitoring |
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