Coefficient of Conservatism:
Coefficient of Wetness:
R. W. Smith
Wet shores and banks, shallow water of ponds and streams, interdunal pools and swales, sedge mats, ditches; often in rather alkaline habitats.
This is a remarkable species in its variable leaf forms, which have been the subject of extensive physiological investigation. Most recently, both photoperiod and submergence have been demonstrated to play major roles in its heterophylly. Submersed shoots always produce dissected leaves, while aerial shoots produce dissected leaves under short days but simple leaves under long days (e.g., as summer progresses). High light intensity and high temperature, however, can at least partly counteract the effects of submergence. Since these plants tend to grow in areas of fluctuating water level (often shallow ponds, swales, and ditches), the series of leaf forms, including transitional states, can be quite varied on a single stem.
Even vegetative, completely submersed, dissected-leaved plants can be readily distinguished from Myriophyllum by the consistently alternate arrangement of the leaves and their relatively broader rachis; the internodes usually bear glandular-looking blackish flecks or spicules.