Eurasian Watermilfoil

[Swede]

Eurasian watermilfoil is a perennial plant native to Europe, Asia, and Africa and was probably brought to the U.S. as an aquarium plant. Today it is considered one of the most aggressive and problematic plants in the U.S. because of the dense colonies which it forms. The stems are multi-branched, somewhat reddish in color, with gray-greenish feather-like leaves. The leaves are in whorls of 3 to 5 around the stem with each leaf divided into 12 or more pairs of thin thread-like leaflets. Reddish flowers are borne on leafless spikes that rise above the surface a few inches. Eurasian watermilfoil can spread from seeds or by fragmentation.

http://aquaplant.tamu.edu/database/submerged_plants/eurasian_watermilfoil.htm