Description: A rather nondescript species of soft limestone rock surfaces and occasionally mortar, virtually absent from the hard limestones of the west. Its powdery chalk-white thallus is often what first draws the eye. The hard, round discs (perithecia) can be immersed or sessile with a raised pore or ostiole clearly visible at the centre. The discs are easily loosened and often fall out leaving empty pits in the rock. Such is its tolerance of soft limestone habitats it has been known to spread to calcareous soil.

Key Identification Features:

• Thallus chalky-white, paler in the shade, often immersed; always on soft limestones
• Discs with pronounced pore opening (ostiole) at the top and habit of loosening and parting company with the thallus.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Verrucaria muralis at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Verrucaria muralis at iNaturalist World Species Observations database.