Eurasian watermilfoil

(Myriophyllum spicatum)

Eurasian watermilfoil is an attractive plant with feathery underwater foliage that is native to Northern Europe and Asia. Eurasian watermilfoil spreads most commonly by stem fragmentation and runners. The plant roots on the bottom, but survives and is spread as free-floating plants waiting to take root. Eurasian watermilfoil also spreads by seeds. The leaves each have 12 to 21 pairs of leaflets and are 1 inch long. The plant is typically submerged with stems to 4 m long, becoming emerged only while flowering or after stream or canal draw down when moisture is present. The flowers occur from June to September and are pinkish and whorled with emerged bract-like leaves just below each whorl. The leaves are bract-like, opposite, 1 to 3 mm long, lanceolate, smooth-margined to finely toothed. Fruits are 4 ribbed or grooved and ultimately break apart into 4, one-seeded nutlets. Eurasian watermilfoil starts spring growth before other native aquatic plants making it very invasive. The plant forms very dense mats of vegetation on the surface of the water that interferes with power generation and irrigation by clogging water intakes. These mats also interfere with recreational activities (e.g. swimming, fishing, skiing, boating, etc.) and create a mosquito habitat and reduce native vegetation.

Eurasian watermilfoil fact sheet