Chemistry, ethnobotanical uses and biological activities of the lichen genus Heterodermia Trevis. (Physciaceae; Lecanorales; Ascomycota): A comprehensive review

Lichens are composite organisms comprised of a photobiont (an alga or a cyanobacterium) and a mycobiont (an ascomycete or basidiomycete fungus) and represent a stable, ecologically obligate symbiotic association. The lichen genus Heterodermia Trevis (Physciaceae; Lecanorales; Ascomycota) is one of the lichen genera distributed worldwide. The thallus is foliose, dichotomously or irregularly branched and the genus Heterodermia differs from other foliose lichen genera in the family Physciaceae mainly on the basis of its prosoplectenchymatous upper cortex in combination with atranorin (a cortical lichen substance). In this review, an attempt is made to compile data (by referring books, journals and various search engines such as Google Scholar, PubMed, and ScienceDirect) available on the chemistry, traditional uses and biological activities of species of Heterodermia. Atranorin and zeorin are the major metabolites found in Heterodermia species. Besides these, salazinic acid and norstictic acid are also found in several Heterodermia species. Heterodermia species are used ethnobotanically as a flavoring agent, in preparation of perfumes and for treatment of wounds and infections. Literature survey revealed the potential of extracts and isolated constituents of Heterodermia species to exhibit biological activities such as antimicrobial, antioxidant, cytotoxic, antinociceptive, anti-inflammatory, insecticidal, immunomodulatory and anthelmintic activity.