A squamulose lichen with olive-grey squamules often obscured by grey-violet soralia found on well lit base rich bark on veteran trees. Can be confused with Parmeliella parvula but this is smaller with the thallus and soralia a similar pale blue-grey colour. Still widespread in the Scottish Highlands, but very rare and declining to the south, probably due to the impact of past acidifying pollution.
Thallus minutely squamulose, crust-like, forming small patches; hypothallus inconspicuous, thin; squamules 2–3 mm diam., often irregularly rounded, contorted, deeply indented; upper surface blue-grey to olive-brown, white felted-tomentose at the margins; soralia grey or violet-grey, granular, mostly on upturned ascending margins, occasionally spreading to the upper surface, often appearing ± woolly (crystals ×50) in dried collections. Apothecia very rare, unknown in British material; disc brown; thalline margin sorediate. Ascospores 13–16 × 7–8 μm, with epispore 16–24 × 8–9 μm; epispore broadly attenuate. Containing fatty acids and steroids, often appearing as crystals on herbarium specimens.
Characterised by the blue-violet colour of the woolly-granular soralia borne on almost lip-shaped lobes of small, often inconspicuous, olive-grey squamules. The soralia are sometimes very abundant, the thallus then becoming an almost entirely grey-violet sorediate crust. Parmeliella parvula resembles the rarer Fuscopannaria mediterranea when sterile, and was mistake for this in the past, but has smaller, (<2 mm), ± elongated, flat to concave squamules, a pale blue-grey coloration, rarely tinged fawn and pale blue-grey soralia.
On base rich bark on broad-leaved trees and on rocks in old growth woodlands.
Locally frequent in the Scottish Highlands, very rare and threatened further south, in N. Wales and Pembrokeshire, S.W. England E. to Hampshire, and S.W. Ireland.
This species appears to have been very sensitive to acidifying pollution and is now very rare south of the Scottish Highlands, although still widespread there, so not assessed as Threatened across Britain. In the south, however, it appears to be in a perilous situation, and reduced to a tiny number of surviving sites.