Description: Thallus crustose, endosubstratic or thinly episubstratic, when well-developed consisting of scattered to contiguous, greenish white to blue-grey, convex to subglobose areoles. Apothecia very rare, micareoid, round, sessile, not constricted at base, up to 0.7 mm across, sometimes confluent into tuberculate, to 1.3 µm wide aggregates, with an ivory white (in shade-forms) or pale to dark grey-black, soon convex disc, and a very thin, soon excluded proper margin. Proper exciple poorly evident, developed only in young apothecia, colourless; epithecium poorly differentiated from the hymenium; hymenium colourless to olive-green or blue-green in upper part, 55-70 μm high, the pigmented parts K- and N+ red; paraphyses conglutinated, branched and anastomosing, 1-1.4 μm thick, the apical cells to 2 μm wide; hypothecium colourless. Asci 8-spored, cylindrical-clavate, the I+ blue tholus with a wide, I+ dark blue tube structure that expands towards the top, without a pale axial body. Ascospores (3-)5-7-septate, hyaline, fusiform-elongate, thin-walled, (19-)23-34(-38) x 4-6 μm. Pycnidia prominent, wart-like, basally immersed in the thallus, paler around the depressed, crater-like ostiolar region, the wall K-. Macroconidia 9-17-septate, flexuous, filiform, 50-110 x c. 1 μm; microconidia narrowly fusiform, to 5 μm long. Photobiont micareoid, thin-walled, the cells 4-7 μm in diam. Spot tests: thallus, apothecial and pycnidial sections K-, C+ red, KC+ red, P- (reactions best visible under the microscope). Chemistry: gyrophoric acid.
Note: a cool-temperate to probably circumboreal-montane species found on the acid bark of deciduous and coniferous trees and on epiphytic bryophytes, in humid montane to subalpine forests, more rarely on lignum of fallen, decorticated trunks and on siliceous pebbles. The Italian distribution seems to be restricted to the Alps.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)