Description: This species is a Lecanora chlarotera lookalike which grows mainly on basic-barked trees such as ash and sycamore. Unlike L. chlarotera it has a distinctly cracked and warted thallus above a white prothallus and glossy orange or brown discs often aggregated into clusters. The red-brown epithecium has a top layer of fine granules (in L. chlarotera these are coarse) and a weakly yellow K reaction. In Ireland, the species occurs in Counties Cork and Fermanagh.

Key Identification Features:

• Like L. chlarotera but with a white prothallus, discs crowded into groups, fine granules lying on the epithecium and weak, K+ yellow spot test.
• On basic-barked trees.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Lecanora horiza at iNaturalist World Species Observations database.