This swamp forest is dominated by Alnus glutinosa, with Frangula alnus and Salix cinerea participating in a sparse shrub layer. The herb layer is characterized by a distinct pattern of hummocks and hollows, the former being usually covered by tussocks of Carex elongata, accompanied by mesophytic species, the latter supporting marsh species and in places even some aquatic plants. This association develops in mesotrophic to eutrophic habitats with significant accumulation of undecomposed organic matter. In spring the water table usually rises above the ground level. In the Czech Republic it occurs mainly on waterlogged sites near fishponds and in terrestrializing oxbows at lower and middle altitudes.