Description: Similar to P. coracodiza (described elsewhere) in size and presence of pinpricked holes but is olive green, smooth and shiny with a much cracked thallus. It grows principally on protruding boulders in both rivers and lakes. In Ireland, it is only known from western County Donegal and should be searched for when river levels are at their lowest.

Key Identification Features:

• Like P. coracodiza but has an olive green, minutely cracked thallus
• On protruding boulders in lakes and rivers; the openings to the discs are pinprick-sized.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Thelignya lacustris at iNaturalist World Species Observations database.