Description: Thallus inapparent, not lichenized, the hyphae developing inside the thallus and soralia of Xanthoparmelia-species, causing 0.7-1.5 mm wide necrotic patches delimited by a blackish line. Apothecia arthonioid, immersed in the thallus and soralia of the host, more or less round, 1.5-3 mm across, with a black, convex disc, without a distinct proper margin. Proper exciple poorly developed, not evident; epithecium brown, c. 10 µm high; hymenium colourless to pale brown, 35-40 µm high, I+ red, K/I+ blue; paraphysoids branched, the apical cells enlarged, to 3 µm wide; hypothecium pale brown, c. 50 µm high. Asci 8-spored, broadly clavate to subglobose, semi-fissitunicate, with a large, non-amyloid apical dome, and a distinct ocular chamber, Arthonia-type. Ascospores 1-septate, hyaline, claviform, with more or less equal cells or sometimes with the lower cell narrower, 10-14.5 x 4-5 µm, with a hyaline, amyloid perispore. Photobiont absent. Spot tests: K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a rarely collected species, known from both Americas and Luxembourg; there is an unpublished record from Italy (Sicily, herb. Brackel).