Cerothallia luteoalba  

Thallus crustose, sometimes spreading extensively, grey-white, thin, continuous, uneven, without a cortex, developing a characteristic waxy pruinose ‘tomentum’ of crystals in dried specimens. Prothallus pale or absent. Isidia and soredia absent. Photobiont Trebouxia-like, with globose to ellipsoidal cells 15-30 µm diam.
Anamorph: conidiomata pycnidial, orange-red, often slightly erumpent from the thallus. Conidia 3-4 × ca 1 μm, cylindrical with rounded ends, straight.
Teleomorph: ascomata apothecia, 0.3-0.5(-0.8) mm diam, numerous, crowded, often contiguous, mostly rounded but sometimes slightly crenulate where ascomata are crowded together, immersed at first, becoming superficial. Thalline margin undeveloped, or sometimes thinly enveloping sides of young ascomata. Proper margin orange, becoming excluded, sometimes somewhat paler than the disc in dried specimens. Hymenium bright orange, the disc deeply concave when young and becoming flat to convex when mature. Interascal tissue of paraphyses, sometimes branched in the apical region, lax, the apical and sometimes the penultimate cell often swollen, to ca 4.5 μm diam. Asci (42-) 46-53 x 9.5-13.5 µm, clavate, the apical part (above the level of the ascospores) sometimes slightly attenuated, short-stalked, thin-walled below but with a strongly thickened upper section, with an outer layer that blues in iodine, 8-spored. Ascospores arranged biseriately, (7.5-) 9-10.5 x 4.2-4.8 μm, ellipsoidal, 1-septate, hardly polarilocular, the septum median, ca 1 μm thick, about 1/10 of length of ascospore, slightly constricted in mature spores, hyaline, smooth-walled, without a gelatinous sheath or appendages.
Chemistry: thallus K–, apothecial discs K+ purple.

BLS species page: here.