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Eurasian Watermilfoil - Myriophyllum spicatum
Family: Haloragaceae

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TPIUC

Description

Plants are submersed except the upper flower-bearing portions (unless stranded at times of low water levels). The stem is thickened below the inflorescence to almost double the width of the lower stem, characteristically curved to lie parallel with the water surface. Leaves are whorled, sessile, the submersed ones pinnately dissected into capillary segments. The bracteal leaves or bracts subtending the flowers are reduced. The foliage leaves have a grayish cast, the segments mostly disposed on the slender, commonly branched stem in pairs, or subopposite, and whorled; the leaves with a markedly feathery appearance; upper primary bracts of the inflorescence less than 2.0 cm long, entire, obovate, lower bracts usually toothed, sometimes entire; the lowermost flowers on the inflorescence usually female, a few median ones bisexual, the upper male. The petals are 4, reddish in the bisexual and male flowers, none in the female flowers.

Plants grow beneath the surface of the water, rooted in the substrate. The upper flower-bearing portion of the stem is above the surface of the water. Plants of this species never form turions but in colder climates die back to the root crowns over winter. The species is rhizomatous, branches freely and forms dense mats upon or near the surface of the water. Plants root at the nodes; vegetative fragments may form new plants.

Interesting facts

This species is known to occur in a variety of habits, becoming established in both impoundments and natural waters, sometimes brackish water or in clear, cool, spring-fed rivers.

Problems associated with this species include displacement of native vegetation, disruption of navigation and recreation by the formation of impenetrable mats, and decreased water flow.

The rapid growth rate of this species allows it to cover water surfaces and displace native vegetation..

VIDEO

Links to more information

US Army Corp Noxious Plant Database

Website, video, and graphics by Rob Nelson
For more information on this plant or management please contact US Army Corp of Engineers

 
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