About Myriophyllum spicatum L.
Myriophyllum spicatum L., commonly known as Eurasian watermilfoil, has slender stems that can reach up to 250 centimeters (8.2 feet) in length. Its submerged leaves, which are typically 15 to 35 millimeters long, grow in pinnate whorls of four. Each leaf has numerous thread-like leaflets that are roughly 4 to 13 millimeters long. This species is monoecious, meaning individual plants produce both male and female flowers. Flowers grow in the leaf axils of a 5 to 15 centimeter long spike that stands vertically above the water surface, with male flowers positioned above female flowers on the spike. Each flower is inconspicuous, orange-red, and measures 4 to 6 millimeters long. Eurasian watermilfoil can be distinguished from the closely related northern watermilfoil (Myriophyllum sibiricum) by leaflet count: Eurasian watermilfol has 12 to 21 pairs of leaflets, while northern watermilfoil only has 5 to 9 pairs. These two species can hybridize, and resulting hybrid plants create taxonomic confusion, because their leaf characteristics are intermediate and can overlap with the leaf traits of both parent species. Myriophyllum spicatum occurs in scattered regions across North America, Europe, Asia, Australia, and Africa.
