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.

[4] 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.

All chemical spot tests are negative on P. sciastra, implying the absence of any secondary metabolites (lichen products).

[6] After having been transferred to other genera and sometimes treated as a subtaxon of other species in its taxonomic history,[1] another Swedish lichenologist, Roland Moberg, reclassified it to Phaeophyscia in 1977.