Description: This species grows within the discs of small saxicolous Lecanora crusts. The giveaway clue is the blackening discs of the host and the narrow one-septate spores that can be seen in a squash of the disc. In Ireland, the species is widely dispersed.

Key Identification Features:

• Grows in the small discs of Lecanora crusts; mainly on limestone rock
• The narrow one-septate spores <15µm long is sufficient to distinguish it.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Arthonia apotheciorum at iNaturalist World Species Observations database.