Practically most of the taxonomists working on vascular plants and fungi are using the so-called taxonomic species concept, relying largely on morphological criteria or other observable patterns of discontinuity and assuming that these patterns are reflecting the underlying genetic integrity of species. Such a concept is described in detail here for the genus Usnea. The typologicalview versus the populational view of species are discussed. The diagnostic value of characters used by previous and recent taxonomists of the genus is analysed. The fact that Usnea has such a bad taxonomic reputation is discussed. The use by J. Motyka, author of the world monograph published in the thirties, of characters that are strongly modified by environmental factors together with a typological view of species are thought to be mainly responsible for this. More than 770 names have been published worldwide so far and it is suggested that around 50% are to be considered as synonyms.