Fens are the first stage of development of bogs, where, despite the thickness of the peat layer, which is more than 30 cm, the plants receive most of the nutrients from the groundwater. This habitat type includes the more species-rich part of fens, which mostly feed on calcareous groundwater. Low-growing sedges and brown mosses predominate, and there are many limestone-loving species, including orchids. In Estonia, this habitat type also extends to the species-rich paludifying meadows.
Alkaline fens are more common in Western, North-Western, and Northern Estonia; they are rare elsewhere. The species-rich paludifying meadows are also mainly associated with Western and North-Western Estonia, especially with the Kasari and Pärnu river basins.
In Estonia, includes the eutrophic alkaline fen and the eutrophic paludifying meadow habitat types.