K. Svenska Vetensk-Akad. Handl., n. f. 20, 8: 112, 1884
Distribution: N - TAA (TU-F072499).
Description: Thallus crustose, endosubstratic, inconspicuous, often consisting of subgelatinous green algal clumps surrounding the apothecia. Apothecia arthonioid, black, rounded, flat to convex, 0.1-0.3 mm across, up to 0.1 mm tall, without a proper margin, all parts K/I-. Epithecium dark brown, 7-10 μm high, K+ olive-brown; hymenium colourless to pale yellow-brown, 40-50 μm high, K+ pale yellow-olive; paraphysoids branched and anastomosing, up to 2 μm thick, the apical cells up to 5 μm wide, dark-capped; hypothecium pale o dark brown, 45-55 μm high. Asci 8-spored, subglobose, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type. Ascospores 1-septate, constricted at septum, hyaline (sometimes turning brownish when overmature), ellipsoid to cylindrical-obovoid, 17-22 (-26) x 6.5-9.5 μm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a rare species found on acid bark, rarely also reported from sandy soil, most frequent in northwestern Europe.