Communities of calcareous, petrifying springs of the Alps, the pre-Alpine regions and of the middle European Hercynian ranges and their periphery, forming and colonizing large tufa deposits. When active, tufa springs comprise a hydrosere in which the Cratoneurion plants, and in particular, Cratoneuron spp., are accompanied by fen species such as Carex lepidocarpa and Sesleria caerulea; the latter may physiognomically dominate both the hydrosere and the adjacent xerosere, developed on fossil tufa deposits, in which it is accompanied by Brometalia plants.