Description: This rock-inhabiting ‘scripture lichen’ is a common sight on limestone walls and mortar as well as on more natural limestones. The thallus can vary from pale pink or grey to chalk white. The discs — which look like primitive scribble — consist of individual slits or stars (lirellae) which may occur singly or in groups. In other forms, the discs are bunched together into tight knots. Long ago, forms from different habitats were named as separate species. Today, however, they are treated as one. It is abundant throughout Ireland, occurring frequently on old and ruined buildings.

Key Identification Features:

• The most common Opegrapha species of basic rock and stone, especially man-made substrata, for example, churchyard or cemetery monuments
• Slit or star-shaped scatter of scribble-like discs.

Original text submitted by Simon Davey

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

iNaturalist: Arthonia calcarea at iNaturalist World Species Observations database.