Thallus 1-3 (-5) cm diam., often forming rosettes or scattered, unorientated lobes, closely appressed to the substratum. Lobes (0.5-) 1-3 mm wide, linear to sublinear, indented or sometimes branching towards the apices, divergent, contiguous or overlapping. Upper surface grey-white, ± shining, older parts often obscured by a ± continuous crust of crowded, concolorous or slightly darker cylindrical isidia which may become eroded. Lower surface whitish to pale brown with simple rhizines.
Anamorph: conidiomata pycnidia. Conidia 3.5-4.5 × ca 1 μm, bifusiform.
Teleomorph: ascomata apothecia, infrequent, to 3 mm diam., sessile to semistalked. Disc red-brown, flat and undulating. Thalline exciple isidiate and disappearing. Interascal tissue of unbranched paraphyses, the apices not or little enlarged. Ascospores 6-9 × 5-6 μm.
Chemistry: cortex K+ yellow; medulla C–, K+ yellow, KC–, Pd+ yellow-orange, UV– (atranorin and thamnolic acids).
Assessed by Woods & Coppins (2012) as of Least Concern.
Formerly restricted to ancient Caledonian pine woodlands in Scotland, but now of scattered occurrence in C Wales & N England, and also frequent and spreading in S England. BLS map here.
On acid bark and wood, especially conifer, Betula and Quercus, rarely directly on peat; now frequently found on artificial substrata e.g. worked oak, conifer wood e.g. fence rails.