The genus Lithothelium, with c. 28 species, is characterised by distoseptate ascospores with rounded lumina, unbranched paraphyses (reported to be branched and anastomosing in one species), and cylindrical asci with a conspicuous ocular chamber. The genus is known from most regions of the world; several species are pantropical, and a few appear to be restricted to temperate Europe or North America. Most species are epiphytes, but others grow on limestone, lava or basalt. A world key was provided by Aptroot (2006). The delimitation of the genus with respect to Pyrenula is still an open problem (see Gueidan & al. 2016). The present key includes the only epilithic species known from Italy, plus other 3 epiphytic species which are known from Austria (see Aptroot & Berger 1994) and should be looked for in Italy.

References

Aptroot A. 2006. Three new species of Lithothelium (Pyrenulaceae) from China and Thailand, with a revised world key and annotated list of species. Lichenologist, 38, 6: 541-548.
Aptroot A., Berger F. 1994. Three species of Lithothelium (Pyrenulaceae) found in Austria for the first time in Europe. Herzogia, 10: 71-73.
Gueidan C., Aptroot A., Cáceres M.E.S., Binh N.Q. 2016. Molecular phylogeny of the tropical lichen family Pyrenulaceae: contribution from dried herbarium specimens and FTA card samples. Mycol. Prog. 15, 1: 1-21.

Last modified: April, 18, 2025

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