Anamorph: conidiomata pycnidia, 90-100 µm diam., globose, immersed in the host thallus. Conidiomatal wall ± hyaline to pale brown below, darker brown above, composed of 3-4 layers of isodiametric cells 4-5 µm diam. Conidiogenous cells 9-11 x 3-4 µm, proliferating percurrently. Conidia 5.5-6 x 0.5-1 µm, bacilliform.
Teleomorph: ascomata 0.2-0.3 (-0.45) mm diam., erumpent, in small clusters and sometimes confluent. Disc flat to convex, brown to dark brown, matt or glossy, with an indistinct margin. Exciple 10-30 (-40) µm thick, pale brown to almost hyaline, composed of ± angular cells 3-7 µm diam. Hypothecium hyaline to pale brown, subhymenium hyaline, hymenium hyaline to pale brownish, 55-65 µm tall, epithecium pale brown to brown, 15-20 µm thick. Interascal tissue of thick-walled paraphyses 2-3 µm diam., occasionally branched and anastomosed, the apical cells with small brown-pigmented caps, 3-5 µm diam. Asci 43-55 x 14-19 µm, obovoid, with a conspicuous I+ tholus penetrated by an I- axial body, and with an outer I+ gelatinized layer; 8-spored. Ascospores (13-) 16-18 (-21) x (5-) 5.5-7 µm, fusiform to fusiform-ellipsoidal, the apices acute, fairly thick-walled, smooth, without an epispore, gelatinous sheath or appendages.
Assessed by Woods & Coppins (2012) as of Least Concern.
On thalli of a wide range of Parmeliaceae, especially on species of Parmelia but also Hypogymnia, Platismatia and Xanthoparmelia. Frequently causes necrosis and contortion of the thallus lobes.
Common in Highland Scotland, rarely recorded in Wales and SW England.