Parmotrema tinctorum (Nyl.) Hale
Brazil, photo kindly provided by Adriano Spielmann.
The foliose lichens of the genus Parmotrema are mainly found at mid-elevations, on tree branches or trunks with much light, or on rock. P. tinctorum is characterized by the presence of isidia, its grey colour, and the strong C+ red reaction of the medulla. It often grows in disturbed habitats, on road-side trees or in gardens.