Description: This is an aquatic lichen of the amphibious (semi-submerged) zone of upland acid streams, bearing prominent, large black discs (to 2.5mm diam.). Several related members of the Porpidia tribe can also occur in this habitat, so it is important to cut a slice obliquely through the disc to observe the internal colouration. A Porpidia disc is very like a jam tart (blackcurrant in this case) and it is the layer just below the surface (the epithecium) that will have the vivid, blue-green colouration which is diagnostic. This test can be easily carried out in the field. The creamy-white to orange thallus is also abundantly speckled with tiny structures named pycnidia. Throughout Ireland.

Key Identification Features:

• Thallus without soredia or isidia, discs large, black with a vivid, blue-green epithecium layer
• On periodically submerged rock surfaces in acid streams and frequently flushed, stony ground across moorland; thallus often orange (oxidised), usually with abundant pycnidia.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Porpidia hydrophila at iNaturalist World Species Observations database.