Mysterious World of Lichens: Highlights on Their History, Applications, and Pharmaceutical Potentials

Background: Lichens play an important role in many ecosystems and exist as a symbiotic association between fungi and algae or cyanobacteria. This symbiosis results in the production of unique secondary metabolites known as lichen substances, which arise within the thalli and are typically in crystal form on the surface of the fungal hyphae. Recently, lichens and their secondary metabolites have been receiving increased attention due to their nutritional value and pharmaceutical potential. Objectives: This review aims to cast a light on the importance and variety of common lichen substances (secondary metabolites), which are investigated along with their historical and contemporary applications, use in environmental research and discussion of the commercialisation of lichens-based products. Methods: The literature, including research and review articles, was analysed and the information was compiled to provide a complete review of Lichens. A desk-based study to elucidate the role of lichens in commercial products was also undertaken. Results: The analysis of metabolites, mostly secondary metabolites, has yielded a wide range of interesting compounds with biological activities from antimicrobial to anticancer. 31 of these compounds are discussed in detail. Further, the nutritional value of lichens is identified alongside a role in environmental monitoring and a number of commercialised lichen-based products are located. Conclusion: Lichens are found on every continent and have a history of use as food, medicine, dyes and livestock feed. The pharmaceutical potential of lichens is high and several companies are now attempting to commercialise these unique attributes.