Myriophyllum aquaticum (Vell.) Verdc.

U.S. Nativity: Exotic
Habit: Aquatic

Synonym(s): parrotfeather watermilfoil, water-feather, Brazilian water-milfoil, parrotfeather

Myriophyllum aquaticum is an herbaceous, rooted, submerged to emergent plant that invades aquatic habitats throughout much of the United States. Stems are stout and blue-green in color.
Leaves are abundant, whorled, pinnately compound, and finely dissected. Submersed leaves are 0.6-1.4 in. (1.5-3.5 cm) long and have 20 to 30 divisions per leaf. Emergent leaves are 0.8-2 in. (2-5 cm) long, less divided and greener than the submersed leaves.
As only female plants occur in North America, reproduction occurs vegetatively. Inconspicuous flowers are formed in the axils of the emergent leaves in the spring (sometimes fall).
No fertile fruit is known to be produced in the United States.
Ecological Threat
Myriophyllum aquaticum's potential range is yet to be determined. In more southern regions, this plant forms monocultures that clog waterways, impeding recreational and commercial boating activities. These monocultures also disrupt the growth of native aquatic plants and provide breeding areas for mosquitoes. Myriophyllum aquaticum is a common water garden plant, which has the potential to escape into local waterways. Control of this plant is extremely costly.

Identification, Biology, Control and Management Resources

Invasive Plant Atlas of New England - University of Connecticut
Global Invasive Species Database - Invasive Species Specialist Group
Plant Invaders of Mid-Atlantic Natural Areas - National Park Service and U.S. Fish and Wildlife Service