Pachnolepia pruinata  

Thallus effuse and often wide-spreading, white to pale grey or pale brown, matt or powdery, rimose-cracked and 0.1-0.3 mm thick but sometimes warty and to 1 mm thick.
Anamorph: conidiomata pycnidia, 100-200 μm diam., rare, ± immersed, pale or red-brown, internally convoluted, the wall hyaline or pale red-brown (K+ pale green). Conidia 10-16 × ca 0.5 μm, thread-like, usually curved.
Teleomorph: ascomata arthonioid apothecia, to 1 mm diam., rounded or angular, sometimes elongate or substellate, immersed, pink to dark brown but usually thickly white-pruinose and hence inconspicuous when dry; 100-250 (-250) μm tall. Epithecium red-brown, K+ grey or pale green. Hymenium 40-60 μm tall, hyaline. Hypothecium 45-85 (-170) μm tall, hyaline. Interascal tissue of numerous anastomosing pseudoparaphyses 1-2 μm diam., in the epithecium often with brown walls and to 2.5 μm diam. Ascospores 13-22 × 4.5-7 μm, (3-) 4- to 5-septate, cylindric-ovoid, the upper cell not enlarged, hyaline, old ascospores apparently never brown.
Chemistry: thallus and apothecia pruina C+ red, K–, Pd–, UV– (arthoniaic acid).