Description: This rare and much overlooked species occurs on rock and soil. The thallus is chalky white, thin to thick. The species is often sterile but is then told by the frequent presence of prominent, black, smoothly rounded spots or pycnidia (up to 0.4mm diam.). When fertile, the elongate discs (slit-like lirellae) can occur in untidy heaps. Under the microscope the spores have on average, three to five evenly-spaced divisions.

Key Identification Features:

• Thallus can be thin or thickly chalky; pycnidia frequent
• Lirellae, often heaped; exposed north-facing stonework and soils.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Opegrapha areniseda at iNaturalist World Species Observations database.