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This species is restricted to south-west Ireland where it grows in seepage tracks on sheltered siliceous rock near the coast. The cracked thallus is grey-brown and the spherical discs (perithecia) are black. Spores are persistently seven-septate, 37–52µm long, but only 3–5µm wide. It is this last feature which truly distinguishes it from P. guentheri var. guentheri which has wider spores as well as a greater variation in spore septa.
Original text submitted by Vince J. Giavarini