Myriophyllum heterophyllum

Variable Water-milfoil

(VARIABLE LEAF MILFOIL, TWO LEAF MILFOIL, RED FOXTAIL)

NOT NATIVE TO MAINE - INVASIVE

NOTE: All leafy milfoils display a wide range of vegetative variability, none perhaps more so than variable water-milfoil. All milfoils found in Maine waters should be considered “suspect” as potential invaders until a positive identification has been confirmed.

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. Infestations of variable water-milfoil may render waters unsuitable for boating, swimming, fishing, and other recreational uses.

Description: Variable water-milfoil is a submersed, aquatic plant that often characterized by a dense “bottle brush” appearance and thick, robust reddish stems. Feather-like divided leaves are arranged in densely packed whorls. (Some the leaves in the whorl may be slightly offset.) There are generally 4 to 6 leaves per whorl and 5 to14 pairs of thread like leaflets on each leaf. The plant produces spike-like flowers that emerge above the surface of the water from mid to late summer. The bracts and flowers are whorled. Minute white flowers develop in the axils of the bracts. The bracts are typically deeply toothed, blade-shaped and more than twice the length of the tiny flowers. The flower spikes are often essential to confirming species identification. Winter buds (or turions) are formed in the fall at the base of the stems or on the rhizomes.

Origin and Range: Native to Europe and parts of the US, though not native to New England. Variable water-milfoil is present in all New England states except Vermont. A variable water-milfoil hybrid (M. heterophyllum x M. pinnatum) has also been confirmed in Maine. The hybrid is considered to be as invasive (and possibly more invasive) than the parent, variable water-milfoil.

Annual Cycle: Variable water-milfoil over winters by hardy roots, rhizomes and turions. Whole plants may also over winter, sprouting new shoots from viable stem tips in the spring. This species does not flower every year, making positive identification challenging. In such cases it is possible to confirm identification using DNA analysis. Plants may regenerate from seed, but also spread readily through root division, fragmentation or turions. The 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.