Description: Wherever there are smooth-barked trees, the trunk, branches and large twigs should be inspected for this ‘black and white’, crustose species. The rather thin, grey-yellow, mazy thallus bounded by a black line, scattered with near jet-black rounded discs (0.3-1.3mm diam.) are its chief attributes. Only in brightly-lit situations might it be confused with Lecidella elaeochroma var. elaeochroma. A squash of the discs under a microscope will show the brown one-septate spores perfectly in Buellia. A dab of Potassium hydroxide (K) gives a clear yellow reaction in B. disciformis compared with the Lecidella which is smudgy yellowish. It is common in the north and west, but largely absent from the south-east of Ireland.

Key Identification Features:

• Greyish thallus scattered with groups of round, black discs bounded by a black margin
• Smooth-bark lichen, K + yellow; spores brown, one-septate.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Buellia disciformis at iNaturalist World Species Observations database.