Description: This crustose lichen with relatively large, convex, deep orange discs on a white or grey thallus that is mostly below the surface of the rock, is an uncommon species except on hard limestone outcrops. In suitable habitats throughout Ireland.

Key Identification Features:

• Large (to 1.5mm diam.), convex discs — often in shallow pits — reacting K + crimson, on a whitish-grey thallus
• The un-margined discs separate it from Caloplaca. All other Protoblastenia species, bar one, have flatter, less brightly coloured discs that may be in deep pits; they also lack the white, immersed thallus
• The newly described Protoblastenia lilacina, that occurs in similar habitats, is very close, but when cut through is lilac coloured internally. This latter species has not yet been recorded in Ireland, but should be looked for.

Original text submitted by Simon Davey

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

iNaturalist: Protoblastenia calva at iNaturalist World Species Observations database.