Medicine[edit]
Lichens have been used in nonscientific traditional medicine practices of many cultures. Historically in Europe, Lobaria pulmonaria was collected in large quantities as "Lungwort", due to its lung-like appearance (the doctrine of signatures suggesting that herbs can treat body parts that they physically resemble). Similarly, Peltigera leucophlebia was used as a supposed cure for thrush, due to the resemblance of its cephalodia to the appearance of the disease.[45]
Lichens produce metabolites proven useful in the medical community.[124] Most metabolites produced by lichens are structurally and functionally similar to broad-spectrum antibiotics while few are associated respectively to antiseptic similarities.[125] These organic acids are the metabolic byproducts of Crassulacean acid metabolism, the means of photosynthesis by lichens.[126] Usnic acid is the most commonly studied metabolite produced by lichens and has been associated with the suppression of tuberculosis.[125] It has also proven bactericidal against Escherichia coli and Staphylococcus aureus and is considered an antimicrobial agent.[127]
A 2011 article published in PLoS ONE indicates that a serine protease isolated from certain species of lichen degrades prions, suggesting a potential application in treating bovine spongiform encephalopathy.[128][129]