Ochrolechia xanthostoma

Thallus thin, white to pale grey, very thin, areoles smooth or rimose-cracked, shiny (perhaps with an epinecral layer), eroding leaving a few flat to concave areoles between rock crystals; prothallus inconspicuous. Ascomata in warts, strongly resembling species of Pertusaria, 0.4–0.5 (–1.5) mm diam., irregularly semi-globose, constricted at the base, smooth, often crowded. Apothecia 1-3 (-6) per wart; visible as pink dot-like depressed poriform discs 50–100 μm diam., often surrounded by a thick shining pink to pale brown rim, with a thin thalline cuff below; epithecium red-brown, K– colourless. Asci 4-spored. Ascospores 55–75 (–85) × 30–40 μm, colourless, becoming brown when old, wall 1–1.5 μm thick, uniform, smooth. Thallus C–, K–, KC+ rose-pink, Pd–, UV+ brilliant white (alectoronic and α-collatolic acids). 

Distinguished by the globular fertile warts with several pinkish ‘ostioles’ closely resembling a species of Pertusaria. The only British specimen identified as Pertusaria trochiscea (from Scotland; Aberdeen, Peddie’s Hill), on mosses overgrowing serpentine, is incorrectly identified; it has been considered to be a race of O. xanthostoma lacking alectoronic acid (UV–, TLC).