Sphagnum-rich Betula pubescens or Betula carpatica woods of the boreal and nemoral western Palaearctic in which Molinia caerulea is accompanied by a cortège of acid fen species, in particular, Carex rostrata, Carex nigra, Carex echinata, Juncus acutiflorus, Agrostis canina, Narthecium ossifragum, Calamagrostis canescens and by ericoid shrubs, in particular Vaccinium uliginosum. Depending on water level, regime of inundation, history of ligneous colonization and nature of the initial stage, the undergrowth may be dominated by Molinia caerulea, by sedges Carex spp., by rushes Juncus spp., by Scirpus cespitosus or by ericoid shrubs, resulting in a number of rather distinctive habitats. Conifers, mostly Picea abies, may participate in the canopy of boreal, northeastern nemoral, Hercynian sub-boreal and pre-Alpine communities; Pinus sylvestris has its westernmost relict stations in northwestern stands. Fennoscandian formations have a number of northern species, in particular Calamagrostis purpurea, Cornus suecica, Empetrum spp., Rubus chamaemorus.