Adiantum capillus-veneris (Maidenhair Fern) along the Vale of Glamorgan Coastline, South Wales, UK: a comparison of surveys over 30 years

Adiantum capillus-veneris (Maidenhair Fern), occurs on all continents except the Antarctic, and is considered stable worldwide (Lansdown & Bilz, 2013). In the UK the vascular plants red data list reports the status of A. capillusveneris as of ‘least concern’ (Cheffings et al., 2005). Native populations occur mainly in crevices or on tufa deposits, limited to a few scattered coastal localities (Stewart et al., 1994). Wales is home to about 25% of the UK’s native population (Dines, 2008) mainly concentrated along the Vale of Glamorgan Coastline and to a lesser extent in Pembrokeshire and Carmarthenshire. The earliest record (Llwyd, 1698), at Jacksons Bay, Barry Island suggest populations have been persistent for at least 300 years. Historical records for A. capillus- veneris can also be found for Porthkerry; 1838, Dunraven Bay; 1849, Aberthaw; 1862 and Font-y-Gary, 1927 and A. capillus-veneris is still present at all of the aforementioned sites. A. capillus-veneris’s natural habitat in South Wales is primarily restricted to active post glacial tufaceous cliff face seepages which are frequently, but not entirely, associated with the Jurassic Lias bedrock that defines the Vale of Glamorgan ‘Heritage Coast’. The interbedded nature of the Jurassic Lias rocks, with relatively impermeable, thinly interbedded limestones and calcareous mudstones (Wilson et al., 1990), favours the slow diffuse seepage of groundwater across large areas of cliff face supporting the formation of tufa. Tufa forms when groundwater, supersaturated with calcium carbonate dissolved from the bedrock aquifer, re-deposits the material on contact with the atmosphere. Three surveys across the Vale of Glamorgan coastline have been undertaken, the first by Peter S. Jones (1983-4) then Kate Pryor 1996 (reported in Pryor, 2001) and again in 2015 by the authors. Molecular studies of several populations along the coast (Pryor, 2001 & Pryor et al., 2001) provide insight into the genetics of satellite populations, however further discussion of this is outside of the scope of this note. The aim of this survey was to collate and compare the locations of populations recorded over the last 30 years. It is hoped that this will serve as a useful baseline for repeat surveys in the future.