Eurasian Watermilfoil (Myriophyllum spicatum)

Eurasian Watermilfoil, Myriophyllum spicatum, invasive, plant, aquatic

Aquatic green perennial that is submersed in water with finely dissected leaves. It becomes limp when removed from water. It can grow up to 4 metres in depth. The leaves are arranged in whorls of four around each node of the stem. The flower can grow up to 20cm above the water and is reddish in colour. Each leaflet has 14-24 hair-like, paired divisions that resemble feathers. There are native milfoils but they have different numbers of leaflet divisions.


Habitat & Ecology

Eurasian milfoil thrives in nutrient rich, slow-moving waters of ponds, lakes, reservoirs, canals, ditches and other waterbodies.


This invasive milfoil spreads through the release of aquarium contents into ecosystems as well as hitch-hiking on boats, trailers and gear between waterbodies. It forms dense stands and shade out native vegetation. These stands can also degrade water quality, clog canals and reduce recreational activities.


It is difficult to manage milfoil because it is an aquatic plant that reproduces by seed and fragments of roots. It can produce up to 300,000 seeds per plant that remain viable for 20 years. It is best to keep areas well vegetated to reduce spread. There is also 3 biocontrols that have been used to reduce seed production and stand density. They are all beetles, 2 that eat the leaves and one that bores into the stem and roots.


Oregon Sea Grant. 2014. On the Lookout for Aquatic Invaders: Identification Guide for the West. Oregon State University.