Description: This freshwater lichen is a member of the ‘submerged zone’ lichen flora of rivers. It is characterised by immersed discs and a dark green to brown-black, subgelatinous, sparsely-cracked thallus, with constellations of small black specks (punctae) in the matrix of the cortex. In acid rivers and stream courses there is nothing with which to confuse it. It is tolerant of shaded river stretches where it often grows intermixed with other species of freshwater Verrucaria. In Ireland, it is scarce, though there are several records from the Dingle peninsula, County Kerry.

Key Identification Features:

• Thallus dark green-brown to black; barely cracked with a scatter of speck-like punctae
• Usually exposed during periods of low water levels; the discs (perithecia) are immersed and seen as tiny black dots.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Hydropunctaria rheitrophila at iNaturalist World Species Observations database.