This is the first attempt to provide an overview of the lichen diversity of the Alps, one of the biogegraphically most important and emblematic mountain systems worldwide. The checklist includes all lichenised species, plus a set of non- or doubtfully lichenised taxa frequently treated by lichenologists, excluding non-lichenised lichenicolous fungi. Largely based on recent national or regional checklists, it provides a list of all infrageneric taxa (with synonyms) hitherto reported from the Alps, with data on their distribution in eight countries (Austria, France, Germany, Liechtenstein, Monaco, Italy, Slovenia, Switzerland) and in 42 Operational Geographic Units, mostly corresponding to administrative subdivisions within the countries. Data on the main substrates and on the altitudinal distribution are also provided. A short note points to the main ecological requirements of each taxon and/or to open taxonomic problems. Particularly poorly known taxa are flagged and often provided with a short description, to attract the attention of specialists. The total number of infrageneric taxa is 3,163, including 117 non- or doubtfully lichenised taxa. The richness of the lichen biota fairly well corresponds with the percent of the Alpine area occupied by each country: Austria (2,337 taxa), Italy (2,169), France (2,028), Switzerland (1,835), Germany (1,168), Slovenia (890) and Lichtenstein (152), no lichen having ever been reported from Monaco. The number of poorly known taxa is quite high (604, 19.1% of the total), which indicates that, in spite of the Alps being one of the lichenologically most studied mountain systems worldwide, much work is still needed to reach a satisfactory picture of their real lichen diversity. Thirteen new combinations are proposed in the genera Agonimia, Aspicilia, Bagliettoa, Bellemerea, Carbonea, Lepra, Miriquidica, Polysporina, Protothelenella, Pseudosagedia and Thelidium.
Keywords: Europe; biodiversity; fungi; lichenised fungi; taxonomy.