Placynthium nigrum  

Thallus to 12 cm diam., often smaller, wide-spreading, brown-black to jet black, ± grey-violet pruinose. Prothallus blue-black, conspicuous, sometimes fimbriate. Thallus of small crowded flat squamules 0.4-1.5 mm diam., with minutely lobed margins, scattered over the prothallus or more usually crowded forming areoles 1-2.5 mm diam. Marginal squamules not enlarged. Lower surface and associated rhizine-like hyphae dark blue-green. Isidia often dense, granular to coralloid. Photobiont cyanobacteria.
Anamorph: no information available.
Teleomorph: ascomata apothecia, 0.5 (-1) mm diam., ± sessile. True exciple black, shining, often becoming flexuose. Disc brown to black, concave, later flat or weakly convex. Epithecium blue-green. Hymenium I+ blue. Interascal tissue of paraphyses, septate, simple or sparingly branched near the tips, apical cells pointed and thickened. Asci cylindrical, Peltigera-type, 8-spored. Ascospores (7-) 9-18 (-22) × 3.5-5.5 (-6) μm, narrowly ellipsoidal, sometimes curved, 1- to 3-septate, fairly thin-walled, smooth, without an epispore, gelatinous sheath or appendages.