Thallus effuse and wide-spreading, or forming small, poorly delimited patches amongst other species, thin, ± continuous, pale grey and rather scabrid or (especially on smooth bark) with scattered areoles on a dark, thin, blue-grey prothallus. Soralia usually numerous, efflorescent, discrete, 0.2-1 mm diam., or often confluent, pale yellowish-green to blueish grey; soredia 30-80 (-100) µm diam., external hyphae often blue-grey, N+ red. Photobiont chlorococcoid.
Chemistry: thallus, medulla and soralia C–, K–, KC–, Pd–, UV+ white (perlatolic acid).
Assessed by Woods & Coppins (2012) as of Least Concern.
On smooth bark easily recognized by the conspicuous, uniform blue-grey colour of the thallus and its soralia: on rough bark and wood often confused with Loxospora elatina or Violella fucata which have K+ yellow-brown, Pd+ yellow-orange or red, UV– soralia. Buellia griseovirens often has a bluish tinge, but its soralia are smaller, excavate, K+ and Pd+ yellow or reddish and UV–. Fuscidea pusilla, F. viridis, Hertelidea botryosa and Lecidea nylanderi all occur on acid bark or wood and have poorly delimited soralia with identical reactions, due to the presence of divaricatic or perlatolic acids, however none of these species has a blue-grey pigment in the prothallus or soralia.
N & W British Isles, extending locally to SE England. BLS map here.
On smooth and rough acid bark and occasionally wood, rarely on shaded siliceous rocks (vertical surfaces), mainly in woodland; common in the west, very rare elsewhere.