Description: Probably better known by its previous name Arthopyrenia halodytes (the barnacle lichen), this species rose to fame following work on the lichens of the intertidal zone. The thallus and black spherical discs (perithecia) are entirely immersed in pits in calcareous rock or more unusually, in the shells of barnacles, limpets and other intertidal shellfish. To the naked eye this species appears to be little more than a scatter of tiny dots which, when squashed, release, one-septate spores. The related C. sublitorale has its discs superficial with a black ± spreading lid (involucrellum). C. foveolatum is well distributed around the coast of Ireland.

Key Identification Features:

• Black dots scattered across the surface of shoreline barnacles and shellfish
• Thallus immersed, perithecia with a lid-like involucrellum only, barely spreading.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Collemopsidium halodytes at iNaturalist World Species Observations database.