Ochrolechia tartarea

Ochrolechia tartarea is a species of saxicolous (rock-dwelling) crustose lichen in the family Ochrolechiaceae. It forms thick, greyish crusts with a rough, crumbly surface marked by irregular warts, typically found on acidic rocks in moist, upland environments across Europe and parts of Asia. The lichen produces distinctive reproductive structures (apothecia) that appear as rounded, pale brown to orange-pink discs up to 5 mm across, often densely packed across its surface. Originally described by Carl Linnaeus in 1753 as Lichen tartareus, it was historically significant as the source of cudbear, a red dye that was commercially important in 18th-century Scotland before overharvesting led to population declines. The species is widespread in the oceanic and mountainous regions of Britain and Ireland, extends through the Alps of central Europe, and has been recorded as far east as South Korea, though it becomes rare in lowland areas and is often confused with similar species.

Taxonomy

Ochrolechia tartarea was first formally described by the Swedish naturalist Carl Linnaeus in his 1753 work Species Plantarum, where he gave it the name Lichen tartareus. Linnaeus characterised the species as a crustose lichen with a whitish to greenish thallus and rounded fruiting bodies (apothecia) that were yellowish at the edge. He distinguished it from related lichens by features such as a pale marginal zone (prothallus) and by comparison with earlier descriptions and figures published by Dillenius and Micheli. At the time, Linnaeus placed it in the broad catch-all genus Lichen, which included nearly all known lichens. After having been transferred to various genera in its taxonomic history, Abramo Bartolommeo Massalongo reclassified it in the genus Ochrolechia in 1852.