Description: This lichenicolous lichen is parasitic on the thallus of Diploicia canescens. The host thallus develops a tight speckling of discs so causing visible brown spots to appear on the surface. The four-spores asci at once distinguish it from other species of the genus. In Ireland, it appears to occur only in western counties.

Key Identification Features:

• Clusters on minute black spots on Diploicia canescens
• Four-spored asci.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Arthonia diploiciae at iNaturalist World Species Observations database.