Description: The discs of this species have the colour and consistency of a black, well-sucked fruit gum, so is smooth, shiny and shaped into an oval. Of course they are many magnitudes smaller (to 1.5mm diam.) and grow in heavily shaded situations at the base of acid-barked trees such as oak. It is photophobic (light-hating) so frequently occurs only on trees in dense shade (spindly broadleaved plantations for example) where it may form monocultures. In Ireland, it has a scattered distribution with a strong population in the drier south-east.

Key Identification Features:

• The shiny, rounded to oval fruits that are relatively large compared with lookalike species serve to indicate this species
• When poorly developed, it can resemble Arthonia didyma from which it can only be separated reliably by microscopic examination of the spores but which also have much smaller discs.

Original text submitted by Simon Davey

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

iNaturalist: Diarthonis spadicea at iNaturalist World Species Observations database.