Thallus endolithic, grey to blackened, strongly contrasting in colour with the apothecium margin. Apothecia 0.5-1.4 mm diam., widely dispersed to partly crowded, sessile to constricted, margin 0.05-0.15 µm thick, white or faintly yellow, sometimes with a blue pigment, smooth, farinose or slightly crenulate; disc pale to grey-brown, not or slightly pruinose; epithecium granular K–, N–, pigment dissolving, without crystals; paraphyses as in L. albescens. Thallus C–, K–, Pd–, UV–; apothecium margin C± yellow, K+ yellow, KC+ yellow, Pd–, UV+ yellow or bright orange (vinetorin).
On calcareous rocks, especially hard limestone. Common and widespread in Britain and Ireland, but not distinguished until recently.
Specimens with a yellow colour on the thalline margin and the UV+ orange rather than bright yellow reaction were previously referred to Lecanora xanthostoma. Often confused with Myriolecis dispersa which differs in the absence of a UV reaction, the white, never black, thallus and the more crowded, never blued apothecia. See also M. crenulata.
Scratchpads developed and conceived by (alphabetical):
Ed Baker,
Katherine Bouton
Alice Heaton
Dimitris Koureas,
Laurence Livermore,
Dave Roberts,
Simon Rycroft,
Ben Scott,
Vince Smith