This alliance includes vegetation in calcareous fens with low primary productivity, composed mostly of short sedges and bryophytes. The fens are fed by ground water and occur either around sloping springs or in areas of seepage in valleys. Calcicole species prevail and Sphagnum mosses do not occur at all because of high pH, calcium and hydrogencarbonate content. Substrates can be either organic peat or, more often, mineral sediments such as calcareous tufa, marl or lacustrine chalk. In sediments rich in calcium carbonate, limitation by available phosphorus and iron strongly affects species composition. In the most water-saturated fens with deep peat layers, some tall sedges with boreal distribution may occur. Some calcareous fens originated already in the late glacial and may have persisted through forested stages of the Holocene, at least in small patches. Some other localities originated after forest clearing in modern times. This vegetation type has a large proportion of specialists and is often dominated by some of them. It is strongly endangered due to habitat destruction, drainage and eutrophication. The decline of traditional mowing practices, which may balance the effects of slight drainage and slight increase in nutrient avaliability, contributes to loss of these fens. The geographical range of this alliance includes temperate Europe.