Description: This very rare epiphyte of holly in western and south-western Ireland is a specialist ravine-woodland species. The thallus is grey or creamy white surrounded by a brown line. The black, non-pruinose discs (to 0.7mm diam.) are rounded but soon fracture from the centre outwards. Under the microscope the muriform spores have two to three longitudinal divisions (septa).

Key Identification Features:

• A species of western ravine-woodland; holly favoured as host
• Creamy white thallus, discs black, rounded, unfrosted, disintegrating at the centre; spores, muriform with two to three longwise divisions.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Arthothelium orbilliferum at iNaturalist World Species Observations database.