Caloplaca crenulatella

Often grows with the superficially similar Protoblastenia rupestris. Thallus greyish-yellow, usually thin and rimose but well-grown specimens can be subsquamulose. Apothecia typically scattered, sessile, 0.5-0.8 mm diam., the margins paler than the disc. Occurs on calcareous rocks, concrete and mortar, and can be frequent in nutrient-rich sites.

Not listed by Alan Orange in Flora of Glamorgan (Wade et al, 1994).