The subcosmopolitan genus Usnea Adans. is among the richest within the Parmeliaceae, including several hundred taxa. The distinction of species, however, is often problematic: many of the described species seem to be connected by a continuous array of transitional forms, and most of the herbarium material is wrongly identified or labelled just as Usnea sp., even in the rather well-investigated Europe. The clarification of species concepts in this genus by Clerc (1984a,b, 1987, 1991, 1992, 1998a, b, 2004, 2006, 2007, 2011a, b, 2013, 2016), Clerc & Naciri (2021), Halonen & al. (2000) and the keys to European species by Randlane & al. (2009) and Clerc & Otte (2018) have contributed to a better knowledge of this genus, also in Italy where it is still very insufficiently studied. The molecular phylogeny by Articus (2004) showed that the genus includes three main clusters of species, which brought to the acceptance of further three genera: Dolichousnea (J. Ohmura) Articus, Eumitria Stirt., and Neuropogon Nees & Flot., which we prefer to treat as subgenera. A recent molecular study by Mark & al. (2016) tried to assess the monophyly of 18 species from section Usnea occurring in North America and Europe, including sorediate and sexually reproducing taxa with both pendent and shrubby thalli; the resulting clades partly represent traditional morphology-based species (Usnea cavernosa, U. praetervisa (as U. parafloridana, see Clerc & Otte 2018), U. silesiaca, U. viktoriana (as U. praetervisa, see Clerc & Otte 2018), and U. wasmuthii), while others cluster two or more species together. Molecular data also did not support the distinction between the fertile U. florida and the sorediate U. subfloridana (Articus & al. 2002, see also Degtjarenko & al. 2020), but here we prefer to maintain them as distinct, due both to their different ecology and to the fact that population genomic analyses of RAD-sequences (Grewe & al. 2018) allowed to clearly distinguish two species in a similar case concerning Antarctic Usnea.
The present key, whose structure and descriptions largely derive from previous publications by Ph. Clerc, includes all species of Usnea which were hitherto reported from Italy (see Nimis 2016), plus 2 species whose presence in Italy is possible, for a total of 29 infrageneric taxa.

References

Articus K. 2004. Neuropogon and the phylogeny of Usnea s.l. (Parmeliaceae, Lichenized Ascomycetes). Taxon 53, 4: 925-934.
Articus C., Mattsson J.-E., Tibell L., Grube M., Wedin M. 2002. Ribosomal DNA and b-tubulin data do not support the separation of the lichens Usnea florida and U. subfloridana as distinct species. Mycol. Res., 106, 4: 412-418.
Clerc P. 1984a. Contribution à la révision de la systématique des Usnées (Ascomycotina, Usnea) d'Europe I. Usnea florida (L.) Wigg. emend. Clerc. Cryptogamie. Bryol. Lichénol., 5: 333-360.
Clerc P. 1984b. Usnea wirthii - a new species of lichen from Europe and North Africa. Saussurea, 15: 33-36.
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Clerc P., Naciri Y. 2021. Usnea dasopoga (Ach.) Nyl. and U. barbata (L.) F. H. Wigg. (Ascomycetes, Parmeliaceae) are two different species: a plea for reliable identifications in molecular studies. Lichenologist, 53: 221-230.
Clerc P., Otte V. 2018. Usnea viktoriana (Ascomycota, Parmeliaceae), a new European taxon of the Usnea barbata-dasopoga group, with a key to the shrubby-subpendulous sorediate Usnea species in Europe. Lichenologist, 50, 5: 513-527.
Degtjarenko P., Mark K., Moisejevs R., Himelbrant D., Stepanchikova I., Tsurykau A., Randlane T., Scheidegger C. 2020. Low genetic differentiation between apotheciate Usnea florida and sorediate Usnea subfloridana (Parmeliaceae, Ascomycota) based on microsatellite data Fungal Biology, 124: 892-902.
Grewe F., Lagostina E., Wu H., Printzen C., Lumbsch H.T. 2018. Population genomic analyses of RAD sequences resolves the phylogenetic relationship of the lichen-forming fungal species Usnea antarctica and Usnea aurantiacoatra. MycoKeys, 43: 91-113.
Mark K., Saag L., Leavitt S.D., Will-Wolf S., Nelsen M.P., Tõrra T., Saag A., Randlane T., Lumbsch H.T. 2016. Evaluation of traditionally circumscribed species in the lichen-forming genus Usnea, section Usnea (Parmeliaceae, Ascomycota) using a six-locus dataset. Organisms Divers. Evol., pp. 1-28.
Nimis P.L. 2016. The Lichens of Italy. A Second Annotated Catalogue. EUT, Trieste, 739 pp.
Randlane T., Törra T., Saag A., Saag L. 2009. Key to European Usnea species. Bibl. Lichenol., 100: 419-462.

Last modified: June, 27, 2023

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