Beach and Dune - Gower - page 158

FIG 87. The bee orchid, occasionally found in the dune slacks. (Harold Grenfell)
FIG 88. Fen orchid. The dune systems of South Wales hold more than 90 per cent of the British population. (David
Painter)
Also found at Whiteford, the petalwort Petalophyllum ralfsii is a rare and vulnerable species, widely
but sparsely distributed in Britain. Due to weather conditions it varies greatly in abundance from year to
year and may disappear from view completely in the summer, surviving as underground tubers. The main
threats are loss of habitat due to dune stabilisation and natural succession and, due to its rarity in this
country,thecollectionofspecimensbynaturalists.Othernotableplantsoftheduneslacksincludeadder's
tongue Ophioglossum vulgatum , a fern that also grows in woodlands and old pastures, round-leaved win-
tergreen, which is a nationally rare plant, and the dune gentian, which is confined to a small number of
sites in South Wales.
Thedunegentian(Fig.89)hasdeclinedovermuchofEuropeandisconsideredtoberareordeclining
throughout its range; at each known site it is currently limited to a small number of damp slacks. As it
is an annual species population sizes vary from year to year. Some years there can be extremely large
numbers of plants. In 1994, for example, a good year, it was estimated that there were more than 5,000
dune gentians at Oxwich. In habitats that have not been affected by deliberate changes in the vegetation it
seems that the species has declined in response to stabilisation. Interestingly, a comparison of the genet-
ic material of the dune gentian with the autumn gentian, alongside which it often grows, has shown that