Description: This common lichen forms white or greenish-white to silvery-grey crusts on trees (rarely on rocks), covered with a thin layer of floury soredia (clusters of fungal hyphae and algae). The surface can often appear scurfy with whitish tramlines, as if browsed by snails. Discs are rare, white and blend with the colour of the thallus. With experience it can be easily recognised, but beginners may wish to apply a small drop of potassium hydroxide (K) to the thallus, which on contact turns yellow then red. Common across Ireland: well-lit trees, especially in woodlands and by waysides.

Key Identification Features:

• White, scurfy patches on well-lit tree bark
• Discs usually absent; K+yellow-red reaction.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Phlyctis argena at iNaturalist World Species Observations database.