Coenogonium luteum  

Thallus crustose, evanescent or thin, effuse, ± unevenly scurfy, pale grey-green, occasionally orange-grey when fresh. Photobiont Trentepohlia.
Anamorph: conidiomata pycnidia, half to three-quarters immersed in the thallus, 150-250 µm diam., pale yellowish, the wall colourless. Conidiogenous cells 5-9 × 1.8-2.5 μm, arising singly or several together from branched supporting cells, cylindrical or bottle-shaped. Conidia 3-4(-5) × 1.5-2(-2.5) μm, ellipsoidal, aseptate, colourless, sometimes biguttulate.
Teleomorph: ascomata apothecia, 0.4-2 mm diam., sessile, distinctly constricted at the base, marginate, concave at first but becoming flat or slightly convex, bright yellow-orange with paler, often flexuose margins, but apothecia may be almost colourless and translucent in very wet conditions. Thalline exciple absent. True exciple colourless, mostly pseudoparenchymatous. Hymenium 50-90 μm high, I+ blue. Interascal tissue of occasionally branched, distinctly septate paraphyses 1.5-2.5 μm diam., usually branched near the apex with a pair of ± swollen apical cells to 4.5 µm diam. Asci 8-spored, narrowly cylindrical, wall thin, K/I+ blue, Catillaria-type. Ascospores (6-) 8-11 x (2-) 2.5-3.5 µm, ellipsoidal, 1-septate, colourless, smooth, without a perispore.
Chemistry: no lichen products detected by t.l.c.