Description: This rare, crustose aquatic lichen forms scurfy-black, much cracked thalli (1-3cm long) on flat, slabby rock along the edges of rivers and streams. It grows just above the submerged zone and is best sought for on hands and knees when stream or lake levels are low. The thallus is dotted with pinprick-sized holes which are the openings to the discs (to 0.5mm diam.). Spores are simple; broadly ellipsoid. On siliceous rocks; it is known from Counties Donegal and Galway. More recently, I have collected this species from the shores of Lough Coumshingaum, County Waterford.

Key Identification Features:

• Tiny, crustose lichen, forming scurfy-black patches (thalli) pinpricked with holes (the discs)
• Along the margins of lakes and rivers, but only visible at low water levels.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Forssellia concordatula at iNaturalist World Species Observations database.