419 The Diversity of Lichenology: Jubilee Volume. A. Thell, M. R. D. Seaward & T. Feuerer (eds). Bibliotheca Lichenologica 100: 419–462. J. Cramer in der Gebrüder Borntraeger Verlagsbuchhandlung, Berlin · Stuttgart, 2009. Key to European Usnea species Tiina RANDLANE, Tiiu TÕRRA, Andres SAAG & Lauri SAAG Institute of Ecology and Earth Sciences, University of Tartu, Lai Street 38, 51005 Tartu, Estonia; e-mail: tiina.randlane@ut.ee Abstract: A key for 32 Usnea species which have been reliably recorded in Europe is presented; short descriptions, extrapolated distribution maps and photographs of diagnostic characters are provided for each species. Introduction The genus Usnea Dill. ex Adans. is a large and cosmopolitan genus which includes macrolichens with an easily recognized beard-like morphology. It is among the richest genera in species within Parmeliaceae, including several hundreds of taxa. The distinction of species, however, is a very complicated task, and exact numbers are unknown for major areas of the world, even for the comparatively well-investigated Europe. About 30 lichen checklists and floras of European countries published during the last 15 years were investigated, and a list of 32 reliably recorded Usnea species was compiled; this list will certainly increase in the future. A few locally reported species which have not been seen by the authors or characterized sufficiently in the literature (e.g. U. anatolica Motyka, U. bithynica Motyka and U. czeczottiae Motyka from Bulgaria; U. decora Motyka and U. krempelhuberi Motyka from Spain; U. fascinata Bystrek from Poland, U. hookeri Motyka from Romania, U. subfaginea Nádv. from Austria), and thereby in need of further taxonomic investigation, are not included in the current study. Our aim was to compile a practical key for identification of Usnea species in Europe. Therefore, the key was deliberately built up on the easiest characters or combinations of characters where possible, although such simplification can cause misidentifications in the case of specimens with untypical character states, which are not rare in this genus. The same key is provided in three different forms: (a) an interactive dichotomous key with numerous photogrpahs and more detailed information on the treated taxa; (b) a traditional, single-access dichotomous key with maps of extrapolated distribution patterns in Europe and photographs of diagnostic characters for each species; (c) a multi-access synoptic key; the first, interactive internet version is available at: http://www.ut.ee/ial5/k2n/key/usnea _eu/index.html) while two latter versions are presented in this paper. A glossary of the main terms used in the keys together with brief explanations, supported by colour images, is provided.