Oligotrophic or meso-oligotrophic, acidocline Alnus glutinosa woods of fens and poorly drained banks of brooks or small rivers of western Europe, mostly characteristic of siliceous regions and Atlantic climates, south to Galicia. Betula pubescens and Frangula alnus often accompany the alders. The ground layer is usually rich in Sphagnum spp. and includes Carex laevigata, Equisetum sylvaticum and many ferns, including Oreopteris limbosperma, Blechnum spicant, Athyrium filix-femina, Dryopteris cristata and Dryopteris carthusiana.