Variable leaf milfoil

Myriophyllum heterophyllum · Aquatic plants

Underwater · Photo: Zac Peterson / CC BY

InvasiveSubmerged

Also called Twoleaf watermilfoil, Variable watermilfoil

State noxious weed listing

Idaho: Early detection

How to identify Variable leaf milfoil

Feathery submersed leaves in whorls of 4 to 6 on thick stems
Stiff emergent flower spike with small, toothed, undivided leaves
Densely crowded leaves give a bottlebrush look

Similar plants

Native watermilfoils have thinner stems and lack the dense bottlebrush look; the emergent spike with toothed bracts is the best clue.

Growth profile

Growing season	Grows from spring through summer, raises flower spikes in midsummer and overwinters as green stems and root crowns.
Starts growing	About 50 to 55 F water
Light	Tolerates moderate turbidity
Depth	1 to 10 feet
How it spreads	Stem fragments, rhizomes and seeds
Habitat	Ponds, lakes and slow streams with soft bottoms; established in western Washington.

Why it matters in a lake

Listed for early detection in Idaho and not known from Idaho, Oregon or Wyoming. Commonly sold in the aquarium trade, which is a likely way it could arrive.