ABSTRACT
Chemistry has had an important role in the taxonomy of lichenized ascomycetes since the early years of lichen systematics, when lichens were distinguished by obvious differences in color which are caused by different secondary metabolites, or characterized by their bitter taste due to the presence of some secondary metabolites. Lichens are symbiotic organisms typically comprised of a fungus and a photosynthetic partner, which may be a cyanobacterium or green alga or both. Morphologically three main growth forms of lichens can be distinguished: crustose, foliose, and fruticose. The introduction of chromatographic methods has made chemical investigations an integral part of any modern taxonomic study in lichenology. Chemotaxonomy was given a much sounder basis by the extensive studies of Asahina and co-workers in the 1930s to 1960s, but the main disagreement on the ranking of chemical variants remained. Many studies have concentrated on phenolic substances and their significance in the distinction of species.
