Description: This species grows only on the thallus of Thelotrema lepidinum on hazel. Small dark patches are the first clue as to its presence. Black discs of various rounded shapes occur sprinkled across the surface containing mostly three-septate spores (11–14µm long), these with an enlarged upper cell. In Ireland, it is known from Counties Sligo, east Donegal and Fermanagh.

Key Identification Features:

• Thallus darker than the host with small, black rounded or elongated discs; spores two- or three-septate with an enlarged upper cell
• On Thelotrema lepidinum on hazel.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Arthonia thelotrematis at iNaturalist World Species Observations database.