Description: Caloplaca microthallina is a small, attractive, yellow-orange maritime species occurring in both the splash zone and upper littoral zone of siliceous and calcareous coastal cliffs. It consists of tiny scales minutely lobate towards the margins, amongst which are scattered, conspicuous orange discs. It grows best on the black thallus of Verrucaria maura, but is not parasitic on it. It is common in suitable habitats in Ireland, especially in the south and west.

Key Identification Features:

• Its small size, tiny rosette-forming lobules, relatively large discs and habit of overgrowing Verrucaria maura should suffice for identification
• Caloplaca marina is a brighter orange, but the edge of the thallus is never lobate.

Original text submitted by Simon Davey

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

iNaturalist: Flavoplaca microthallina at iNaturalist World Species Observations database.