South Gower Cliffs - Gower - page 81

Plantago coronopus , thrift Armeria maritima , sea campion, scurvygrass Cochlearia officinalis , sea beet
Beta vulgaris ssp. maritima and the only maritime fern, sea spleenwort Asplenum marinum. Sea spleen-
wort rarely grows far beyond the immediate spray zone and the most luxuriant plants only occur on the
lower parts of the most exposed cliffs. In Gower it occurs in small numbers in crevices, overhangs and
caves and is rather sparsely scattered along the coast. The saltwater spray it receives is important since it
allows the fern to benefit from the winter warmth brought by wave-splash, the sea acting as a giant ra-
diator that warms and cools very slowly, minimising the occurrence of frost to which sea spleenwort is
extremely susceptible.
There have been few descriptions of the lichen flora of Carboniferous Limestone in Britain, so it is
worth describing the situation on the Gower cliffs in some detail. The communities appear to be rather
species-poor, with many western species absent. Well-illuminated limestone on the vertical faces of the
cliffs is typically dominated by small crustose lichens that form small-scale mosaics, including Xanthoria
aureola, Ramalina siliquosa and the orange crustose lichens of the genus Caloplaca (Fig. 42). One spe-
cies, C. granulosa , although frequently found in Gower, is extremely rare in the rest of Britain. On damp
surfaces, with a slight to moderate degree of shading, these lichens are largely replaced by species such
as Acrocordia conoidea , Dermatocarpon miniatum and in some areas the rarely recorded Leptogium dif-
fractum . Despite the standard outcrops of rock having a relatively limited species diversity, a wider range
of species exists in microhabitats, such as underhangs. Underhangs not receiving direct rain, for instance,
are well colonised by a thick white form of Direina massiliensis f. sorediata , the thalus of which contains
copious amounts of calcium oxalate. Associated species include Caloplaca ochracea , Diploicia canes-
cens and the small dispersed thalli of Placynthium garovaglii .