This class includes vegetation of tall-growing, competitively strong annual wetland herbs. Most stands are monodominant and species poor. It occurs in both natural and man-made, wet and nutrient-rich habitats such as river banks, muddy alluvial sediments, desiccating oxbows, bottoms of summer-dried fishponds, wet ditches, wet forest clearings, wet arable fields, edges of dung hills and places with agricultural waste water input. This class is distributed across Eurasia and North America, being particularly common in wet areas. Most associations of this class have spread since the second half of the 20th century due to eutrophication.