Rhizocarpon is a genus of c. 250 crustose species in the Rhizocarpaceae. Although predominantly free-living, a substantial minority of species are parasitic on other lichens, at least early in their development, and a few are even non-lichenised. The genus is most diverse and abundant on siliceous rocks in montane habitats and at temperate to high latitudes; it is much less represented or completely absent in the wet and dry tropics and subtropics and in hot-arid regions. Molecular studies (e.g. Ihlen & Ekman 2002) have shown that the genus in its current circumscription constitutes a polyphyletic group, which can only be made monophyletic if R. hochstetteri is excluded or Poeltinula, and perhaps also Catolechia, are included (the present key also includes Catolechia). The subgenera Rhizocarpon and Phaeothallus are artificial as well (see e.g. Roca-Valiente & al. 2016). In Europe, the yellow species were monographed by Runemark (1956), the brown species with multicellular spores by Feuerer (1991). A key to European species with yellow thallus was provided by Poelt & al. (1988), an overview of parasitic species by Poelt (1990). Important recent information on the brown species was provided by Fryday (2000, 2002) and by Ihlen (2004). The separation among species is problematic in some groups, and according to Roca-Valiente & al. 2016), several species and subspecific taxa of yellow Rhizocarpon- species, especially in the Rhizocarpon geographicum-complex (which, pending a general revision of the entire group, I still maintain here in the traditional sense) proved to fall within a wide concept of Rh. geographicum. The present key includes 68 infrageneric taxa, i.e. those known to occur in Italy (see Nimis 2016), plus several species which are known from adjacent areas, especially in the Alps (see Nimis & al. 2018), and which should be looked for in Italy.

References

Feuerer T. 1991. Revision der europaischen Arten der Flechtengattung Rhizocarpon mit nichtgelbem Lager und vielzelligen Sporen. Bibliotheca Lichenologica 39, 218 pp.
Fryday A. 2000. On Rhizocarpon obscuratum (Ach.) Massal., with notes on some related species in the British Isles. Lichenologist, 32, 3: 207-224.
Fryday A.M. 2002. A revision of the species of the Rhizocarpon hochstetteri group occurring in the British Isles. Lichenologist, 34, 6: 451-477.
Ihlen P.G. 2004. Taxonomy of the non-yellow species of Rhizocarpon (Rhizocarpaceae, lichenized Ascomycota) in the Nordic countries, with hyaline and muriform ascospores. Mycol. Res., 108, 5: 533-570.
Ihlen P.G., Ekman S. 2002. Outline of phylogeny and character evolution in Rhizocarpon (Rhizocarpaceae, lichenized Ascomycota) based on nuclear ITS and mitochondrial SSU ribosomal DNA sequences. Biol. J. Linnean Soc., 77: 535-546.
Nimis P.L. 2016. The Lichens of Italy. A Second Annotated Catalogue. EUT, Trieste, 739 pp.
Nimis P.L., Hafellner J., Roux C., Clerc P., Mayrhofer H., Martellos S., Bilovitz P.O. (2018) The lichens of the Alps - an annotated checklist. MycoKeys 31: 1-634. h
Poelt J. 1990. Parasitische Arten der Flechtengattung Rhizocarpon: eine weitere Übersicht. Mitt. Bot. Staatss. München 29: 515-538.
Poelt J., Černohorský Z, Schaefer J. 1988. Rhizocarpon Ram. Em. Th. Fr. Subgen. Rhizocarpon in Europe*, Arctic and Alpine Research, 20:3, 292-298.
Roca-Valiente B., Hawksworth D.L., Pérez-Ortega S., Sancho L.G., Crespo A. 2016. Type studies in the Rhizocarpon geographicum group (Rhizocarpaceae, lichenized Ascomycota). Lichenologist 48, 2: 97-110.
Runemark H. 1956. Studies in Rhizocarpon. I. Taxonomy of the yellow species in Europe. Opera Botanica 2(1): 1-152.

Last modified: November, 18, 2023

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