Coefficient of Conservatism:
Coefficient of Wetness:
Ponds and lakes, including the Great Lakes and connecting waters.
This Eurasian species, our commonest non-indigenous water-milfoil, was first found in North America late in the 19th century, but did not become a serious aquatic weed until the mid-20th century. It was first recognized in Michigan in 1970 but had been collected in 1961 in St. Clair Co. and may well have been present well before then but confused with M. sibiricum. It is now an aggressive weed in many lakes and streams, where it crowds out other species. The plant spreads primarily by fragmentation.
Many characters have been proposed to distinguish this species from M. sibiricum, but of the easily seen morphological ones, only the number of leaf segments (on well-developed leaves) seems reliable. In the field, the two look quite different. Myriophyllum spicatum tends to branch profusely near the surface of the water, forming a tangle of foliage that shades plants below. The leaves are strongly feather-like, the segments all in one plane. Rare hybrids with M. sibiricum are known, more or less intermediate in leaf segment number (see Moody & Les, 2007).