calcareous rimmed lichen

Circinaria calcarea is a species of crustose lichen in the family Megasporaceae. It was first described as a new species by Carl Linnaeus in his 1753 work Species Plantarum. Linnaeus named it Lichen calcareus, as he classified all lichens in the eponymously named genus. The species has had an extensive taxonomic history, resulting in dozens of synonyms. In 2010, it was placed in its current genus, Circinaria, following molecular phylogenetic analysis of the Megasporaceae.