Rhizocarpon is a large genus in the Rhizocarpaceae. Although predominantly free-living, a substantial minority of species are lichenicolous, 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 former circumscription, was polyphyletic. Several species have been transferred to other genera by Möller & al. (2015). In Europe, the yellow species were monographed by Runemark (1956a,b), the brown species with multicellular spores by Feuerer (1991). A key to European species with yellow thallus was provided by Poelt & al. (1988), a key to most species of Western Europe is in Clauzade & Roux (1985), an overview of parasitic species by Poelt (1990) (see also Holtan-Hartwick & Timdal 1987), a preliminary key to the species of Scandinavia is in Timdal & Holtan-Hartwick (1988). Important information on the brown species was provided by Fryday (1996, 2000, 2002) and by Ihlen & Ekman (2002) and 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 77 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

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Feuerer T. 1991. Revision der europaischen Arten der Flechtengattung Rhizocarpon mit nichtgelbem Lager und vielzelligen Sporen. Bibliotheca Lichenologica 39, 218 pp.
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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. 1956a. Studies in Rhizocarpon. I. Taxonomy of the yellow species in Europe. Opera Botanica, 2, 1: 1-152.
Runemark H. 1956b. Studies in Rhizocarpon. II. Distribution and ecology of the yellow species in Europe. Opera Botanica, 2, 2: 1-150.

Last modified: September, 22, 2025

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