Description: This lichen is very easily mistaken for P. nigrum. The smaller thallus (to 3cm diam.) of minute pimple-like granules, the broadly ellipsoid spores (to 9µm across compared with 6µm in P. nigrum) and habitat of intermittently submerged rock such as by the edge of lakes, usually serves to distinguish it. In Ireland, the species is very rare and poorly known.

Key Identification Features:

• • Small thallus, dense with granules
• Spores broader than in P. nigrum; habitat of lake margins and particularly tolerant of fluctuating submergence.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Placynthium tantaleum at iNaturalist World Species Observations database.