Highly oligotrophic, strongly acidic communities composed mainly of sphagnum growing on, and forming, peat and deriving moisture and nutrients only from rainfall (ombrotrophic). They form only in cool climates with heavy rainfall and are characteristic of lowlands and hills of northwestern and northern Europe, the adjacent Hercynian ranges, the Jura and the Alps. Their independence from ground water is the result either of upward growth or of changes in the water table. Bogs harbour, in addition to various sphagnum species, which are abundant, dominant and the major component of their formation, a small number of acidophilous plants such as Eriophorum vaginatum, Scirpus (Trichophorum) cespitosus, Carex pauciflora, C. paupercula, Ledum palustre, Vaccinium oxycoccos, Andromeda polifolia, Drosera rotundifolia and lichens. Animal species are not numerous but those that are adapted to bogs are highly specialised. Among typical invertebrates figure dragonflies (Leucorrhinia dubia, Aeshna subarctica, A. caerulea, A. juncea, Somatochlora arctica, S. alpestris), lepidopterans (Colias palaeno, Boloria aquilonaris, Coenonympha tullia, Vacciniina optilete, Hypenodes turfosalis, Eugraphe subrosea), beetles, ants (Formica exsecta), bugs and spiders (Pardosa sphagnicola, Glyphesis cottonae). Most of the species that bogs harbour are rare and their populations fragmented into isolated relictual elements; several are threatened. The remaining intact or nearly intact communities are exceptional.