Pertusaria leioplaca DC.
Thallus crustose, superficial, thin, deeply encrusted within the bark, margin very thin without zonate structure, surface smooth to minutely rimose, typically with small heaps of whitish crystals scattered all over the thallus surface, giving a rime ice or a snowy aspect, pale greyish, pale grey-yellowish, pale grey-greenish to greenish, covered with scattered warts, slightly prominent, globose to conical, apices slightly flattenned and base wider, 0.5-2 mm diam.. Apothecia, 1 or 2 per wart, most often embedded, punctiform, disc dark, hardly visible. Ascii 4-spored, elongate, fragile. Ascospores narrowly ellipsoid, thick walls to 3-5 µm, 50-80 x 25-40 µm. Cortex: C-, K+ yellow, KC+ yellow, Pd+ red-orange (seldom Pd-), UV+ pale orange. Not especially maritime, but common on trees with smooth barks in humid woodlands. N.B. Not to be confused with Thelotrema lepadinum of which the apothecia have a different structure.*