Thallus 10-20 cm diam., rather thick (to ca 1.5 mm). Lobes 10-20 (-30) mm wide and 100 mm long, often imbricate, deeply incised, the margins ± raised, undulate and sometimes inrolled. Upper surface ± even, downy or greasy, brown tinged blue-green when dry, deep blueish olive-green or brown when wet, smooth or often thinly scabrid-tomentose with erect hairs especially towards the lobe margins, usually glabrescent in the central part. Lower surface ± white to pale brown at the margins, becoming brown-black towards the centre, ± uniformly tomentose, veins and paler interstices few and diffuse or absent. Rhizines to 3mm long, sparse, black, bushy or fasciculate, sometimes entirely absent. Photobiont cyanobacteria (Nostoc).
Teleomorph: ascomata apothecia, rarely developed, on short thalline stalks, 4-8 mm diam., sessile, ± circular, brown-red to dark brown, shallowly convex, ± crenulate at the margin. Ascospores (45-) 55-70 (-90) × (2.5-) 4-6 μm, 3- to 5-septate, elongate-fusiform.
Chemistry: thallus with tenuiorin, methyl gyrophorate, ± gyrophoric acid (C+ red) and unidentified terpenoids (as those found in P. leucophlebia).
Assessed as Endangered (B) by Woods & Coppins (2012). It is considered Nationally Rare, and is a (former) BAP Priority Species listed for protection under the Nature Conservation (Scotland) Act 2004. It appears to be reasonably common in its stronghold in the Culbin Forest, but ongoing surveys would be valuable.
Distinguished by the continuous, non-veined, grey to dark brown, felted underside, scarce rhizines and vertical, hair-like tomentum on the upper side of the thallus especially toward the margins. The species has been confused with Peltigera neckeri, which lacks the tomentum on the upper surface.
In GB&I, confined to eastern Scotland. Records from VC95 Moray, VC96 E Inverness and VC107 E Sutherland, with outlying populations in VC80 Roxburgh and VC85 Fife.
On the ground in acid coastal dunes and conifer plantations, very rarely inland.