Hydropunctaria rheitrophila

Hydropunctaria rheitrophila is a widely distributed species of crustose lichen in the family Verrucariaceae. It grows on rocks in aquatic environments, typically in streams and rivers where it colonizes silica-containing substrates that are regularly submerged or wetted. The lichen forms a thin to thick crust-like body (thallus) that ranges in colour from pale brownish green to dark green, often dotted with black spots. It is widely distributed throughout the Northern Hemisphere, particularly in Europe, North America, and Asia, with some occurrences in the Southern Hemisphere including New Zealand. Originally described in 1922 as a member of the genus Verrucaria, it was reclassified in 2009 as part of the newly established genus Hydropunctaria, which includes several aquatic lichen species. ...read more on Wikipedia.