Petractis clausa  

Thallus crustose, effused, endolithic, whitish or yellowish-white, sometimes with scattered blue-grey flecks. Photobiont Scytonema.
Anamorph: not seen in GB&I material.
Teleomorph: ascomata apothecia,  400-700 µm diam., usually paler than the thallus, flat to shallowly convex, urceolate, immersed, leaving pits in the rock when decayed, developing below a circular thalline cover which splits radially from a central pore as the structure expands. Thalline margin ± persistent, 10-15 μm wide, ± expanding to 30 μm in the uppermost part, initially covering the apothecia, with (3-) 4-6 (-8) distinct radiating fissures developing at maturity, disintegrating with age. Disc pinkish to pale orange or pale yellow-orange when moist, sometimes drying reddish-brown. True exciple pale, thin, inconspicuous, detached from thalline cover when dry, composed of conglutinated narrow hyphae. Hymenium 200-320 μm tall. Interascal tissue of slender, simple, thinly septate paraphyses 1-1.5 μm diam., scarcely swollen at the colourless apices; periphyses absent. Asci 150-250 × 12-18 μm, ± cylindrical, the wall thin, with a single functional layer, J+ blue; without a distinct apical dome, 8-spored. Ascospores (15-)17-23(-35) × 5-7 μm (excluding the perispore), mostly 3-septate, rarely submuriform, hyaline, fusiform, with a conspicuously fimbriate sheath.
Chemistry: lichen products not detected by TLC.