Arthonia radiata  

Thallus immersed, usually delimited by a brown line and often mosaic-forming, white, pale grey, sometimes with a brown or olive tinge.
Anamorph: conidiomata pycnidia, 60-85 μm diam., rare, immersed, black, the wall brown, K+ pale green. Conidia 4-5 × ca 1 μm, bacilliform.
Telomorph: ascomata arthonioid apothecia, variably shaped, rounded to substellate and 150-800 µm diam., linear or sparingly branched and to 1400 x 100-200 µm, or stellate and to 1.5 (-2.2) mm diam., flat or slightly convex, black, not pruinose. In section 70-100 μm tall. Epithecium brown or olive-brown, K+ pale green. Hymenium 35-50 μm tall, hyaline. Hypothecium 10-25 μm tall, hyalie to pale olive-brown, K+ pale green. Interascal tissue of pseudoparaphyses, numerous, 1-2 μm diam., often to 3 μm diam. and brown-walled in the epithecium, often with dark apical caps. Ascospores 15-20 × 4.5-6 μm, cylindric-ovoid to cylindrical, 3-septate, the apical cell not enlarged.
Chemistry: lichen products not detected by TLC.