Usnea hirta
Usnea hirta is a species of beard lichen in the family Parmeliaceae. It was one of 80 lichen species first formally described by Carl Linnaeus in his 1753 work Species Plantarum. Friedrich [Heinrich Wiggers] transferred it to the genus Usnea in 1780. The lichen is sensitive to air pollution, and is often used as a biomonitor of sulphur dioxide. Usnea hirta has an extensive worldwide distribution, and it is morphologically variable, which has led to numerous intraspecific taxa being proposed in its taxonomic history.