Eurasian watermilfoil

Eurasian watermilfoil
Name	Eurasian watermilfoil
Status	Invasive in many regions
Genus	Myriophyllum
Species	spicatum
Authority	L.

Eurasian watermilfoil is an aquatic flowering plant in the genus Myriophyllum introduced widely outside its native Eurasian range. It forms dense submerged mats that alter physical, chemical, and biological conditions in lakes, rivers, and wetlands, provoking management responses by agencies and stakeholders across North America, Europe, Asia, and Oceania. Research on its ecology, impacts, and control involves collaborations among institutions such as the United States Geological Survey, Environment Canada, Wageningen University, and state or provincial natural resource departments.

Taxonomy and Description

Myriophyllum spicatum was described by Carl Linnaeus and is classified in the family Haloragaceae, within the order Saxifragales. Morphological descriptions appear in floras produced by the Royal Botanic Gardens, Kew and herbaria at the Natural History Museum, London, and Harvard University Herbaria. Vegetative stems can reach several meters and bear pinnate submerged leaves in whorls; reproductive structures include emergent spikes of small flowers that have been documented in monographs and botanical keys from the Missouri Botanical Garden, Smithsonian Institution, New York Botanical Garden, and the Botanical Society of Britain and Ireland. Molecular phylogenetics employing markers used by the Max Planck Institute, Smithsonian Molecular Biology programs, and the Sanger Centre have clarified relationships among Myriophyllum, Najas, Cabomba, and other aquatic genera.

Distribution and Habitat

Native to parts of Europe, Asia, and northern Africa, the species has been recorded beyond its indigenous range on continents documented in atlases produced by the International Union for Conservation of Nature, the Food and Agriculture Organization, and regional agencies such as the California Department of Fish and Wildlife, Ontario Ministry of Natural Resources and Forestry, and Department of Conservation (New Zealand). Introductions are noted in the Great Lakes, Finger Lakes, Sacramento–San Joaquin Delta, and other basins managed by the US Fish and Wildlife Service, Environment Agency (UK), and European Environment Agency. Habitats include mesotrophic to eutrophic lakes, slow-flowing rivers cataloged by the Environmental Protection Agency and Water Resources Authority, and artificial reservoirs engineered by agencies like the Bureau of Reclamation and Australian Department of Agriculture. Dispersal pathways described by research groups at Cornell University, University of Minnesota, and McGill University include ballast water associated with shipping regulated under the International Maritime Organization and fragment transport by recreational boating overseen by Parks Canada and state park systems.

Ecology and Impacts

The plant alters light attenuation, dissolved oxygen cycles, and sediment dynamics studied by researchers at Woods Hole Oceanographic Institution, Scripps Institution of Oceanography, and the Leibniz Institute of Freshwater Ecology. Dense beds provide habitat for invertebrates cataloged by the Smithsonian Institution’s National Museum of Natural History and alter fish assemblages examined by the American Fisheries Society, Fisheries and Oceans Canada, and the Australian Institute of Marine Science. Impacts on ecosystem services have prompted policy responses from the European Commission, United Nations Environment Programme, and state departments such as the Minnesota Department of Natural Resources and Michigan Department of Natural Resources. Economic assessments by the Congressional Research Service, Canadian Economic Development agencies, and New Zealand Treasury describe costs to recreation, hydroelectric facilities managed by the Tennessee Valley Authority, and irrigation infrastructure overseen by the US Army Corps of Engineers. Interactions with native macrophytes such as Potamogeton species and invasive taxa like Hydrilla and Lythrum salicaria have been explored in studies by universities including University of Wisconsin, Ohio State University, and University of California, Davis.

Identification and Similar Species

Identification keys in regional floras prepared by the Royal Botanic Gardens, Kew; Flora Europaea; and Flora of North America distinguish this species from congeners including Myriophyllum sibiricum and Myriophyllum heterophyllum, and from other submerged genera such as Elodea, Vallisneria, and Cabomba. Diagnostic characters used by the Natural History Museum, Royal Society publications, and botanic gardens include leaf pinnule counts, flower spike morphology, and chromosome counts reported in cytogenetic studies from the Max Planck Institute and University College London. Field guides published by the National Audubon Society, Peterson Field Guides series, and state naturalist programs outline tests and characters to separate it from look-alikes and hybrids reported by botanical surveys at Yale University, University of British Columbia, and University of Helsinki.

Management and Control

Management strategies are coordinated among agencies such as the US Geological Survey, Department of Environmental Conservation (New York), Environment and Climate Change Canada, and New South Wales Department of Primary Industries. Integrated approaches combine mechanical harvesting used by municipal utilities, hand-pulling promoted by volunteer groups in national parks and at sites managed by the National Park Service, and chemical control with herbicides registered by the Environmental Protection Agency and Health Canada. Biological control research has included trials with herbivorous insects and pathogens studied by the Centre for Agriculture and Bioscience International, Oregon State University, and the University of Florida. Preventive measures promoted by the Aquatic Nuisance Species Task Force, state boater inspection programs, and international protocols under the Convention on Biological Diversity focus on sanitation, certification schemes, and public outreach implemented by extension services at Michigan State University, University of Minnesota Extension, and Rutgers Cooperative Extension.

Uses and Human Interactions

While primarily regarded as a pest by tourism boards, fisheries agencies, and water utilities like Seattle Public Utilities and Melbourne Water, its role in phytoremediation and experimental wetland restoration has been examined by research teams at ETH Zurich, Wageningen University, and University of Tokyo. Citizen science projects coordinated by iNaturalist, the National Phenology Network, and local watershed groups document occurrences alongside monitoring networks run by the European Environment Agency and United States Geological Survey. Stakeholder conflicts involving angling clubs, marina operators, and conservation NGOs such as The Nature Conservancy, World Wildlife Fund, and local land trusts have driven litigation, policy development, and cooperative management agreements mediated by courts and administrative bodies in jurisdictions including Ontario, California, and New Zealand.

Category:Haloragaceae