Description: This tiny, crustose species has a grey to brown minutely shattered thallus, the pieces (areoles) being about one millimetre across. Each areole supports a small, black disc. It occurs on smooth, acid substrates and is often the first species to be found on undisturbed pebbles and dry stone wall tops, where it may become abundant. On raised beaches, it can become dominant, but it can also occur in towns on loose stones. A dab of Potassium hydroxide (K) may turn it red, but sometimes the reaction is negative.

Key Identification Features:

• Tiny grey to brown crusts on undisturbed, smooth acid rock, the centres packed with angular discs
• There are several similar species to be eliminated
• Buellia stellulata occurring close to the sea is white and can be separated on the K+ yellow reaction. Buellia ocellata occurring in similar habitats has areoles tinged with yellow and is C (fresh bleach) + orange.

Original text submitted by Simon Davey

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

iNaturalist: Buellia aethalea at iNaturalist World Species Observations database.