Porpidiaceae Porpidia tuberculosa Growth type crustose Chemical results negative Common on exposed siliceous rocks, pebbles, walls and memorials, rare on worked timber. Very variable. White to bluish-grey thallus, sometimes with a narrow, dark prothallus. The scattered or crowded punctiform soralia are pale grey or greyish-blue. Black apothecia are occasional. Similar: Porpidia soredizodes. Soredia K+ yellow, C-, P+ orange

Porpidia tuberculosa
November 2013 and January 2016