COUNTRYSIDE COUNCIL FOR WALES
SITE OF SPECIAL SCIENTIFIC INTEREST: CITATION
ANGLESEY CORS ERDDREINIOG
National Grid Reference: SH470820
Site area: 289 ha
Cors Erddreiniog is a large calcareous valley mire of national importance. There are three fen basins interconnected by the drainage system. A Carboniferous limestone escarpment, bearing limestone grassland and a hazel woodland, lies along the eastern side of the main basin. From its foot emerge base-rich springs, associated with which is a rich flora of black bog rush Schoenus nigricans; narrow-leaved marsh orchid Dactylorchis traunsteineri, which has been the subject of taxonomic research; fly orchid Ophrys insectifera - here growing in a most unusual habitat; and columbine Aquilegia vulgaris. This orchid-rich vegetation type, found at a few sites in Anglesey and Lleyn, is not found elsewhere in Great Britain.
Fen dominants include great fen-sedge Cladium mariscus and blunt-flowered rush Juncus subnodulosus; purple moor grass Molinia caerulea is spreading in response to aeration following drainage. Locally there are acidic nucleii with bogmoss Sphagnum spp and cross-leaved heath Erica tetralix. On the ridge between the central and NW fen basins is an acidic heathland with marsh gentian Gentiana penumonanthe in abundance. The site also has a rich insect fauna, particularly of Lepidoptera and Odonata.
(1) CCW manages part of the site as a NNR.