Order: Arthoniales       Family: Roccellaceae Species: Opegrapha vermicellifera Growth type crustose. Photos: Under dead branch of Cork Oak. Ardnagashel, Co. Cork, SW Ireland. Identified by Andy Acton Smooth, light to medium-grey thallus that can form large patches. Usually sterile with small, prominent pycnidia with white or pale grey pruina. Pycnidia semi-immersed when young, chestnut brown with pale ostiole. When fertile lirellae 0.6 to 1.2mm, slender, exciple sometimes furrowed or pruinose. Scarce in Ireland in shaded, dry recesses of basic-barked trees, rarely found on rock. Chemical reactions and UV negative. Similar: Lecanactis abietina, pycnidial pruina C+ red

Opegrapha vermicellifera March 2010