Description: This species forms neat non-pruinose, deep orange crustose rosettes with lobed edges (1–2cm diam.) which like a good red wine may take many years to reach this mature colour from its yellow-orange, more youthful, shade. It grows clamped to the substratum except for a tiny area close to the tip of the lobes. It occupies well-illuminated siliceous rocks near the coast so cannot be mistaken for C. saxicola, which is a calcicole. It is scattered in Ireland.

Key Identification Features:

• An acidophile; it forms small, deep orange crustose rosettes except at the margins which are lobed
• Young thalli are yellow-orange.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Caloplaca arnoldii at iNaturalist World Species Observations database.