Description: Like P. nigrum but thallus often white pruinose, very small (<3cm diam.) and composed of coralloid granules (not squamules). Prothallus poorly developed at the base of the crust; spores persistently one-septate. It grows on damp, shaded hard limestones. In Ireland, the species is known only from Clare.

Key Identification Features:

• Like P. nigrum but thallus smaller, more granular in composition and often with a whitish frosting
• On hard limestone in damp, shady places.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Placynthium tremniacum at iNaturalist World Species Observations database.