Anglesey Fens / Corsydd Môn IPA

Location: East Anglesey, between Benllech and Llangefni, to the west of the A5025.

Grid Reference: SH 500 800


Anglesey Fens IPA has been recognised as one of 165 Important Plant Areas in the UK.

The key features of this IPA are:

  • The species richness of stoneworts in base-rich fens
  • One of the best UK examples of threatened habitats of:
    Alkaline fens;
    Calcareous fens with Great Fen Sedge;
    Nutrient-poor waters with Stonewort algae
  • The Anglesey Fens comprise a series of fen basins located on the limestone of eastern Anglesey. They contain a rare type of wetland fed by alkaline water that drains into the fens from the porous limestone rocks surrounding them. They support the second-largest area of such calcareous fens in the UK. Wetland habitats on peaty soil over sandstone, granite or other chalk-deficient substrates are normally acidic, but the alkaline water draining into these wetlands creates conditions that support a most unusual combination of plants. Many of these plants can exist only in this type of highly alkaline habitat.

    Nationally scarce species may be seen, including the fly orchid which grows on tussocks in Cors Bodeilio and Cors Erddreiniog, and the narrow-leaved marsh orchid. The lesser butterfly orchid, normally associated with open woodland edges or chalky meadows, may be found in Cors Erddreiniog, Together with it you might find six other orchid species growing within a metre of each other: common twayblade, marsh fragrant orchid, marsh helleborine, northern marsh orchid, early marsh orchid and fly orchid. The fly orchid is rare in Wales, and rarer still is the yellow form which also grows here. Anglesey is a well known location for the frog orchid in Wales, and it too occurs here.

    Lesser clubmoss, marsh cinquefoil and the insectivorous butterwort can be found in the fens, and growing on the exposed limestone are other species normally associated with calcareous soils: green-winged orchid, common rockrose and wild thyme. Soil on the more acid sandstone is home to tormentil, spring squill and western gorse. In late summer, areas of acid wet heath support populations of brilliant blue marsh gentians. The best Welsh sites for stoneworts are here and rarities include rugged stonewort (Chara rudis), and hedgehog stonewort (Chara pedunculata).

    Image: Anglesey Fens ©David Woodfall/Plantlife