Ceratophyllum demersum, a submerged aquatic macrophyte, is able to form distinct dormant organs during given periods of the year. The dormant form consists of a stem with short intemodes and whorls of thick, brittle leaves; the normal vegetative form of a stem with long intemodes and slender leaves. In temperate regions the dormant form occurs in winter, the normal vegetative form in summer. Several factors affect the initiation of and the emergence from dormancy.