Xanthocarpia crenulatella  

Thallus crustose, poorly delimited, varying from almost absent to subsquamulose, grey-yellow to yellow, corticate, not shiny or pruinose, thin, flat and rimose.
Anamorph: no information available.
Teleomorph: apothecia to 1 mm diam., bright yellow, becoming crowded, contiguous, rounded and not angular, ± flat. Proper margin surrounded by a slightly warted thalline margin. Epithecium with numerous yellow-brown crystals. Hymenium usually hyaline. Hypothecium hyaline. Interascal tissue of unbranched paraphyses, broadening to ca 4 μm diam. towards the tips. Asci clavate, short-stalked, the apex often ± attenuated, 8-spored. Ascospores 15-17 (-18) × (6.5-) 7-8.5 μm, ellipsoidal, the length/breadth ration rather variable, the wall with an inconspicuous ± median  thickening, the septum variable, usually 1.5-2.5 μm wide and under 1/8 of the length of the ascospore, hyaline, smooth, without an epispore, gelatinous sheath or appendages.
Chemistry: all yellow-pigmented parts K+ purple.