File:A lichen - Usnea subfloridana - geograph.org.uk - 953699.jpg

English: A lichen - Usnea subfloridana. This photograph was taken from the side of a footpath through the coniferous woods. Many conifer twigs here are densely "bearded" with lichens such as this one. Close examination of the lichen's branches through a hand-lens helps to distinguish between the various Usnea species. Of these, U. subfloridana is one of the most pollution-tolerant, and it is a very common and widespread species in Britain. The colour of the lichen arises from the usnic acid that it contains (compare: 945680); this compound has been found to have some useful antiseptic and antifungal properties, but it is also one of the lichen substances that occasionally induce an allergic reaction among some forestry workers [see "Lichen Biology", Thomas H. Nash III].