The flower stem is a rigid pink-flowering spike up to eight inches long that is held erect above the water during flowering. The fruit contains four seeds. The seeds have a fairly low germination rate, but seem to be long-lived. Eurasian watermilfoil generally has twelve or more pairs. The leaves of Eurasian watermilfoil collapse around the stem when it is removed from the water.
Native species are more sturdy and maintain their spread-leaf shape.
Eurasian watermilfoil leaves occur in whorls of four around the stem. This aquatic weed is found in ponds, lakes, irrigation canals, and rivers. It prefers quiet waters, but can be found in flowing and backwater areas of rivers. It tends to grow in waters up to 20 feet deep, depending on light penetration. Most plants are found in waters to 10 feet deep.