This alliance includes vegetation types dominated by perennial or biennial wetland herbs such as Alisma, Butomus, Oenanthe, Rorippa and Sagittaria, or graminoids. They occur in habitats with periodical changes of water level, typically in shallow littoral zones or in fishponds in the years following water drawdowns. Many species regenerate from seed or vegetatively on exposed bottoms, and develop maximum biomass if the period of exposure is followed by a period of shallow flooding. Some species typical of this vegetation have adapted to water level fluctuations by developing dimorphic leaves, with different morphologies produced in submerged and emergent conditions. These vegetation types usually occur in habitats of short duration and soon decline due to either deeper flooding or succession of tall marshes. This alliance is widespread in the temperate zone of Eurasia, with some occurrences in the boreal zone, and has also been recorded in the Americas.