This genus of the Verrucariaceae consists of c. 20 species worldwide, growing on soil, detritus, mosses and algal or lichen crusts, rarely directly on rock. Placidiopsis differs from the closely related Catapyrenium, which has the same type of upper cortex, in having septate ascospores and lacking pycnidia. The distinction between the two genera has been confirmed by molecular data (Prieto & al. 2010, 2012). The genus has been monographed by Breuss (1996), the species of the Iberia Peninsula were treated by Prieto & al. (2010b). This is a key to the 6 species known to occur in Italy (Nimis 2016), plus 2 further species which should be looked for in the Italian Alps. Placidiopsis crassa (Anzi) Clauzade & Cl. Roux is excluded from the key, as according to Breuss (1996) this species does not belong to Placidiopsis; it is probably related to, if not identical with, Placopyrenium formosum Orange (see Orange 2009).

References
Breuss O. 1996. Revision der Flechtengattung Placidiopsis (Verrucariaceae). Öst. Z. Pilzk., 5: 65-94.
Nimis P.L. 2016. The lichens of Italy. A second annotated catalogue. EUT, Trieste, 740 pp.
Orange A. 2009. Two parasitic species of Placopyrenium (Verrucariaceae) from freshwater habitats in north-west Europe. Lichenologist, 41, 2: 131-139.
Prieto M, Martı́nez I., Aragón G., Otálora M.A.G., Lutzoni F. 2010. Phylogenetic study of Catapyrenium s.str. (Verrucariaceae, lichen-forming Ascomycota) and related genus Placidiopsis. Mycologia, 102, 2: 291-304.
Prieto M., Martínez I., Aragón G. 2010b. The genus Placidiopsis in the Iberian Peninsula and the Balearic Islands. Mycotaxon, 114: 463-472.
Prieto M., Martinez I., Aragón G., Gueidan C., Lutzoni F. 2012. Molecular phylogeny of Heteroplacidium, Placidium, and related catapyrenioid genera (Verrucariaceae, lichen-forming Ascomycota). Am. J. Bot., 99, 1: 23-35.

Last modified: April, 12, 2022

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