This alliance includes species-rich vegetation with calcicolous species, calcium-tolerant peat mosses (e.g. Sphagnum contortum. S. teres and S. warnstorfii), species with boreal distribution and shallow-rooting acidophytes. It can occur on old, deep peat sediments, as well as in initial phases of peat formation and on fen grasslands that are cut periodically for low-quality hay. It can also develop from calcareous fens of the alliance Caricion davallianae through autogenic succession associated with peat accumulation and consequent decrease of water table. The habitat is fed by ground water with intermediate pH and calcium content. Outside the Czech Republic, the alliance also includes moss communities with a sparse herb layer, as well as fen woodlands with coniferous trees. That the latter habitat also existed in our region in the late glacial has been confirmed using the fossil record. This alliance contains a large proportion of specialists, endangered species and species considered to be glacial relicts. It occurs across the Eurasian and North American boreal zone and in the mountain ranges of temperate Europe.