Invasive Species (Aquatic) -


Variable-leaf / Two-leaf watermilfoil
(Myriophyllum heterophyllum Michx.)

Photos & Description courtesy of IPANE

What Variable-leaf / Two-leaf watermilfoil does to the habitat

Variable-leaf Watermilfoil, like its relative Eurasian Watermilfoil, can congest waterways and crowd out other species of aquatic plants. The thick stands  degrade the water quality for fish and aquatic wildlife.


Dense growth inhibits boating, swimming and fishing and slows down water flow to create an ideal breeding area for mosquitoes.



You need to be careful to avoid breakage as that can easily spread the problem. Small areas can be cleaned up with a pond rake. There are machines that will harvest large areas, but with this technique you have to be especially careful of not spreading it.


Additives to the water that filter out light work in some areas, but that effects all plants, not just the targets.


The same is true of herbicides. What works will kill both native and invasive species.


Common Name

Full Scientific Name

Variable-leaf watermilfoil
Two-leaf watermilfoil

Myriophyllum heterophyllum Michx.

Family Name Common

Family Scientific Name

Watermilfoil family Myriophyllum heterophyllum


Botanical Glossary

Myriophyllum heterophyllum is an herbaceous aquatic plant that has stout stems up to 3 mm (0.1 in.) in diameter. The leaves are green and in whorls of 4-6. There are two types of leaves. The highly variable emergent leaves are bracts and can reach 10-15 cm (4-6 in.) above the water. These leaves are stiff and can be serrated to lobed along the margins, lanceolate or lance-spatulate to elliptic. These emergent leaves are 0.4-3 cm (0.2-1.2 in.) long and 1.5-5 mm (0.06-0.2 in.) wide. The submerged leaves are feather-like, pinnate, 2-5 cm (0.8-2 in.) long and 2-4 cm (0.75-1.5 in.) wide. They have 4-10 paired pinnae. Mudflat forms have 4-5 paired pinnae. The flowers are small, and the reddish, oval shaped petals are 1.5-3 mm (0.0625-0.125 in.) long. The fruit are subglobose in shape, have a scabrous texture and are 1-1.5 mm (0.04-0.05 in.) long and wide. Each of the mericarps is 2-ridged on the back but rounded on the sides, and is prominently beaked. The fruits and flowers appear from June-September. Page References Crow & Hellquist 194, Fernald 1074, Gleason & Cronquist 309, Holmgren290, Magee & Ahles 772.

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