Thallus wide-spreading, to 5-10 (-20) cm diam. (to 35 cm diam. in Scandinavian material), subcoriaceous, loosely attached. Lobes 10-30 (-40) mm wide and to 10-18 cm long, rounded, the margins ± raised. Upper surface roughened, blue- to brown-green when hydrated, grey-brown to brown when dry, matt, scabrid but not tomentose. Lower surface brown to black-brown with distinct veins in the central region, the veins 0.8-1.2 mm broad, grey to ochraceous brown towards the margins, with the tissue between the veins 1-2 mm broad and similarly coloured. Rhizines 2-3 (-5) µm long, dark brown to black, fibrillose to fasciculate, separate, often growing together at their tips and then forming a ± continuous mat. Photobiont cyanobacteria.
Anamorph: not known.
Teleomorph: ascomata apothecia, not seen in British material; disc 3-6 mm diam., saddle-shaped, dark reddish brown, on shortly extended thalline lobes. Ascospores 75-90 × 3-5 μm, filiform, 3-septate.
Chemistry: thallus with tenuiorin, methyl gyrophorate, gyrophoric acid (C+ red), T1, T2, T3, T6 and two unidentified triterpenoids.
Assessed as Vulnerable (D2) by Woods & Coppins (2012). It is considered to be Nationally Rare, and is listed for protection under the Nature Conservation (Scotland) Act 2006.
Distinguished by its scabrous (not tomentose) upper surface of the thallus, and by the usually strongly veined underside with dark tufted rhizines. P. scabrosella also has a scabrous thatllus, but differs in its smaller thallus with narrower and more acute lobes, the undersurface with an indistinct and paler ochraceous veining pattern and paler, slender and simple rhizines.
Only recorded from two sites in northern Scotland, one on the border between VC105 W Ross and VC106 E Ross, and the other in VC111 Orkney.
On acid soil in montane habitats.