Submersed Plants

Species: Myriophyllum spicatum L., Eurasian milfoil, Eurasian water-milfoil
Family: Haloragaceae

Eurasian milfoil, an invasive non-native plant, is one of the worst aquatic plant pests in North America. Like native aquatic milfoils, it has feather-like underwater leaves and emergent flower spikes. Usually leaf shape and size can be used to distinguish it from other milfoil species. However, Eurasian milfoil is a variable species, often making it difficult to identify without chemical or DNA analysis. Because it is an extremely invasive plant, it is important to distinguish Eurasian milfoil from the native milfoils. Every effort should be made to prevent the spread of this plant.

Submersed Plants Icon
Leaf: Two types. Submersed leaves: 2-4 cm long, feather-like, arranged in whorls of 4 around the stem. The leaves are often square at the tip and typically have greater than 14 leaflet pairs per leaf. On mature plants the leaflets are closely crowded along the midrib. Emergent leaves: tiny (1-3 mm long) smooth edged to toothed, located on the flower spikes with one leaf beneath each flower, leaves shorter than flowers. 

Stem: Long, often abundantly branched stems form a reddish or olive-green surface mat in summer.

Flower: Tiny. On reddish emergent spikes 4-8 cm long. Female flowers lack petals, 4 petals on male flowers, 8 anthers. 

Fruit: Up to 3 mm in diameter, divided into 4 chambers, with 1 seed per chamber.

Root: Many, fibrous, from the plant base. Roots often develop from plant fragments.

Propagation: Plant fragments; rhizomes. Sprouting from seed is rare.

Importance of plant: This invasive plant spreads rapidly, crowding out native species, clogging waterways, and blocking sunlight and oxygen from underlying waters.

Distribution: Native to Eurasia and northern Africa, but is a widespread weed in North America. Found in many lakes and rivers throughout Washington.

Habitat: Lakes, rivers, and ponds. Tolerates a wide range of water conditions.  

May be confused with: Northern milfoil (Myriophyllum sibiricum) whichinvasive, nonnative plant Icon has fewer than 14 leaflet pairs per leaf, generally has stouter stems, and produces winter buds. When lacking flower stalks, Eurasian milfoil is also easily confused with most other milfoils.

Photographs: Closeup photo of Myriophyllum spicatum leaflets

Line Drawings: Myriophyllum spicatum

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