Rare Alpine, peri-Alpine, northern British and periarctic pioneer communities colonizing gravelly, sandy, stony, sometimes somewhat argilous or peaty, calcareous sedimentary substrates soaked by cold water, in moraines and on the edge of springs, rivulets, glacial torrents of the alpine or subalpine levels, or on alluvial sands of pure, cold, slow-flowing rivers and calm backwaters. The highly characteristic constituents, with a boreoarctic or glacial relict distribution, are Carex bicolor, Carex microglochin, Carex maritima, Carex atrofusca, Carex vaginata, Kobresia simpliciuscula, Scirpus pumilus, Juncus arcticus, Juncus alpinoarticulatus, Juncus castaneus, Juncus triglumis, Typha minima, Typha lugdunensis, Typha shuttleworthii, Tofieldia pusilla; they are often accompanied by Carex davalliana, Carex dioica, Carex capillaris, Carex panicea, Carex nigra, Blysmus compressus, Eleocharis quinqueflora, Scirpus cespitosus, Primula farinosa, Equisetum variegatum, Drepanocladus intermedius, Campylium stellatum.