Pier Luigi Nims
This genus of the Stereocaulaceae, with c. 140 species, was monographed by Lamb (1977, 1978). Traditionally, it included lichens with a crustose primary thallus and a fruticose secondary thallus. This view has changed in recent years, as five crustose species completely lacking a secondary thallus have been transferred to the genus; the phylogenetic analysis by Högnabba (2006) supports the inclusion of the crustose species in Stereocaulon (see also Timdal 2002), while the current infrageneric classification is not supported. Furthermore, species concepts need to be re-examined, as some species do not appear as monophyletic entities in the phylogeny.
The present key includes the 13 species known to occur in Italy, plus 6 other entities known from the Alps outside the Italian territory, for a total of 10 infrageneric taxa.

References Högnabba F. 2006. Molecular phylogeny of the genus Stereocaulon (Stereocaulaceae, lichenized ascomycetes). Mycol. Res., 10: 1080-1092.
Lamb I.M. 1977. A conspectus of the lichen genus Stereocaulon (Schreb.) Hoffm. J. Hattori Bot. Lab., 43: 191-355.
Lamb I.M. 1978. Keys to the species of the lichen genus Stereocaulon (Schreb.) Hoffm. J. Hattori Bot. Lab., 44: 209-250.
Nimis P.L. 2016. The lichens of Italy. A second annotated catalogue. EUT, Trieste, 740 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 Catalogue. Mycokeys, 31: 1-634.
Timdal E. 2002. Stereocaulon cumulatum comb. nov., another crustose species in the genus. Lichenologist, 34, 1: 7-11.