In the UK this habitat is defined by stands of saw sedge (Cladium mariscus) in base-rich fen habitats. The habitat can be species-rich, particularly in stands where the saw sedge struggles to achieve dominance. The habitat is rare in the UK and Wales supports only three sizeable areas: in the Anglesey fens, the Lleyn fens and at Crymlyn Bog on the outskirts of Swansea.