Individual narrow, strap-like, convex, pale grey thalli lobes are small but can mass to extend over wide areas. The upper surface lacks the white flecks seen in Physcia caesia or marginal cilia seen in some other species. The marginal lobes can flare out to produce crenately incised apices. The soralia are mostly laminal, convex and can be so abundant as to cover parts of the thallus. The medulla reacts yellow when potassium hydroxide is applied. There is no reaction in the medulla of the similar P. tribacia.
Photo: ©Alan Silverside
This lichen favours well-lit wayside trees with a basic bark close to the coast. It has become much rarer in England following the loss of mature elm trees.
Holm Oaks at Orielton, S. Pembs, 1996 (Photo: Alan Hale)