Description: Thallus crustose, episubstratic, verruculose to granular, grey. Apothecia stalked and pin-like to subsessile, black with a bright yellow pruina on the edge of the capitulum and on the mazaedium, especially in young apothecia. Stalk black, (0.2-)0.6-1(-1.4) mm high, of weakly sclerotized, pale greenish to brown, irregularly interwoven hyphae, the outer layer paler and covered with a thin, transparent, weakly amyloid gelatinous sheath. Capitulum broadly lenticular, with a well-developed, cup-shaped exciple; mazaedium well developed, black; hypothecium dark brown. Asci clavate, formed singly, dissolving early, with 2-3-seriate ascospores. Ascospores 1-septate, dark brown, ellipsoid, 13-17 x 5.5-8 µm, with a thick, distinctly ornamented wall, the ornamentation consisting of spirally arranged ridges. Photobiont chlorococcoid. Spot tests: thallus K+ yellow then red, C-, KC-, P+ yellow-orange; ascomata I-, except the outer layer of the stalk which is weakly amyloid. Chemistry: thallus with norstictic acid; yellow pruina with vulpinic acid.
Note: a holarctic, temperate species found on bark, rarely on lignum of deciduous trees, especially oaks, often in fissures of the bark, more rarely on conifers.