Description: This is a conspicuous siliceous rock-inhabiting lichen of moist, upland, vertical rock faces. It has a white to grey areolate thallus studded with small clusters of short black, stumpy, Graphis-like, slit-topped discs (lirellae). The species has simple spores. Spot tests: K+yellow-red, PD+ orange. The one old record from County Galway is now considered doubtful. A fresh search for the species in Ireland is required.

Key Identification Features:

• K+ yellow-red, PD + orange thallus, white to grey, areolate, 4-5cm diam.; prothallus black, visible between the areoles
• Discs (lirellae) stout, clustered with simple spores; shady vertical walls of siliceous rock in the mountains.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Lithographa tesserata at iNaturalist World Species Observations database.