A crustose species with a pale grey to grey, and often areolate thallus with a prothallus that, when present, is black. Apothecia are sessile, large and sometimes pruinose, with a prominent margin.
Medulla: C-, K+ yellow turning red.
In Scotland, Porpidia platycarpoides is occasionally found on siliceous rocks, especially those along the coast, and on basalt. It is also found on boulders in freshwater habitats. BLS distribution map
scottishlichens.co.uk 