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This distinctive foliose species occurs on basic rock and stone, especially where it is enriched by birds. The grey thallus, browner or greener when wet, forms circular or semicircular colonies with fan-shaped lobes arranged like waves lapping the shore. An icing of pruina over the surface of the lobes is common. The main body of the plant appears to be covered in lines of granules which spread along the lobe edges: these are the soredia which help to identify it. The root-like rhizines that attach the lobes are pale, simple structures. Discs are generally rare. P. grisea is also frequent to abundant on dust-enriched, basic-barked wayside trees. It is evenly distributed throughout Ireland.
Original text submitted by Simon Davey