ABSTRACT
The secondary metabolites of lichens, often referred to as “lichen substances” or “lichen acids”, are one of the more intensively investigated aspects in lichenology. They are routinely used in lichen systematics, more so than chemical substances, of any other group of organisms. The “chemistry” of about one third of all lichen species has been studied and about 350 secondary compounds are known from lichens. Color tests were invented in 1866 by W. Nylander, even before the dual nature of lichens was recognized, and have been used ever since in taxonomic determinations. Thin-Layer Chromatography is a more accurate and very common technique for detecting and identifying lichen substances. A few lichen fragments are crumbled on a microscope slide and extracted with a few drops of acetone. After evaporation of the solvent, the fragments are removed gently leaving a residue of crystals on the slide.
