Phaeophyscia sciastra

Phaeophyscia sciastra, commonly known as the dark shadow lichen or the five o'clock shadow, is a widespread species of foliose lichen in the family Physciaceae. This rock-dwelling species tend to form rosettes on sun-exposed rocks, especially sandstone. The thalli, which grow up to 5 cm (2.0 in) in diameter and are closely attached to their substrate, are made of flat to convex lobes typically up to 0.5 mm wide. The lichen occurs in Africa, Asia, Europe, and North America, and is one of the most widespread members of its genus in boreal and subtropical regions. The prominent characteristic of Phaeophyscia sciastra is the presence of black, granular isidia that occur in both laminal and marginal areas of the thallus. Apothecia (fruiting bodies) occur rarely in this species. All chemical spot tests are negative on P. sciastra, implying the absence of any secondary metabolites (lichen products). Individuals or populations of P. sciastra with longer lobes and that lack isidia tend to resem......read more on Wikipedia.