[Wikipedia] Range, Similarity to Other Milfoil, Invasiveness, Spread: Myriophyllum verticillatum, the whorl-leaf watermilfoil[1] or whorled water-milfoil,[2] is a native to much of North America, North Africa, and Eurasia. It closely resembles another native milfoil, called northern water milfoil (M. sibiricum)[3] Whorled water milfoil is also easily confused with four types of invasive milfoils: Eurasian water milfoil (M. spicatum), Variable water-milfoil (M. heterophyllum), Parrot feather (M. aquaticum), and hybrid water milfoil (M. heterophyllum X M. laxum). In many areas it is an invasive aquatic plant. With the increase in water sports, the spread of many water milfoils (Haloragaceae) has increased over the years. The spread of a milfoil is not only within one area, sometimes it spreads from one area to another many miles away. To the untrained eye, whorled water milfoil can look similar to other species. (link added by Mary Ann Machi)