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.
Assessed by Woods & Coppins (2012) as of Least Concern.
Distinguished from other species of Xanthocarpia by its variable but usually reasonably well-developed yellow to yellow-gray weakly areolate thallus. According to Vondrák et al. (2011) the species is polyphyletic, and the status of GBI material needs further research.
Frequent throughout lowland England and Wales, more rarely recorded from Scotland and Ireland. BLS map here.
On flat concrete such as drain covers and disused airfield runways, rarely on inland limestone.