milfoil

Milfoil, commonly called water milfoil, is a group of aquatic plants in the genus Myriophyllum. The genus includes roughly 60 species found in freshwater and occasional brackish habitats across the world. Milfoils are typically submerged for much of the year, though some species have portions that emerge above the water. They have slender, branching stems with finely divided, threadlike leaves arranged in opposite or whorled clusters along the stem. Leaves are formed into feathery, pinnate structures that can give the plant a lacy appearance. Flowers are small and inconspicuous, produced on slender inflorescences that extend above the water surface in some species.

Milfoils occupy a range of aquatic environments, including ponds, lakes, slow-moving streams, and wetlands. They prefer still to slowly flowing water with adequate light; nutrient levels can vary. Some species form dense stands that hinder boating, fishing, and water flow.

Several milfoil species have become problematic as invasive aquatic plants. The Eurasian water milfoil, Myriophyllum spicatum, is particularly widespread in North America and Europe. It grows rapidly, forms dense mats at the water surface, and can outcompete native vegetation, reducing biodiversity and complicating recreation. Spread is often by plant fragments carried on boats or equipment.

Management relies on integrated approaches. Mechanical removal and dredging can reduce abundance but is rarely permanent. Chemical herbicides such as systemic aquatic formulations may be used where allowed. Biological control using milfoil weevils (Euhrychiopsis lecontei) and, in some regions, milfoil leaf-mining insects are explored as options. Effective control depends on early detection and a combination of methods tailored to the site.