KEYS TO THE LICHENS OF ITALY - 52) POLYBLASTIA and THELIDIUM (with Agonimia, Atla, Halospora, Henrica, and Sporodictyon)

Pier Luigi Nimis
This is a key to all species of crustose or microsquamulose Verrucariaceae with pluricellular ascospores and without hymenial algae known to occur in Italy (Nimis 2016), plus several species known from neighbouring countries in the Alps (Nimis & al. 2018), which should be looked for in Italy, for a total of 93 infrageneric taxa.
The taxonomy of the Verrucariaceae is presently being revised on the basis of molecular data. Gueidan & al. (2007, 2009) and Savić & al. (2008) have shown that morphological features traditionally used for characterising the genera Polyblastia, Thelidium, Staurothele and Verrucaria, such as spore septation and colour, occurrence of hymenial photobionts, involucrellum structure, and substrate preference, are only partially consistent with supported clades, and thus are not always reliable for characterising natural groups. The analysis by Savić & al. (2008) revealed strongly supported groups, such as Polyblastia s.str. and a Thelidium-clade group (a mixture of Polyblastia, Thelidium, Staurothele- and Verrucaria-species). Many nomenclatural changes are expected to occur in these genera in the next future (see also Orange 2013).
The following genera are included in this key:
1) Agonimia - One of the few genera in the Verrucariaceae having dark-pigmented perithecia with multilayered walls, lacking an involucrellum, and with colourless muriform ascospores. It includes a dozen species that grow in shaded, moist places as epiphytes, or on mosses at the base of trees, on roots, rocks and various types of soil or plant debris (see e.g. Hafellner 2014). Good descriptions and a key to the British species are in Orange (2013). A worldwide key to all species of the genus was provided by Breuss (2020).
2) Atla - A recently-described genus recognised on the basis of both molecular and morphological data, to accommodate four species formerly included into Polyblastia (Savić & Tibell 2008). Three further species were added to the genus by Pikälä & Myllys (2016).
3) Halospora - A genus segregated from Merismatium by Hafellner (2011) to include lichenicolous Polyblastia-like species with thick-walled halonate ascospores and ascomata with a typically verrucarialean shape in longitudinal section. Species with thin-walled, non-halonate ascospores (all on calcicolous lichens) are retained in Merismatium. The species are non-lichenised, but were frequently treated as lichens in the past.
4) Henrica - A genus first described as monotypic from Italy, to accommodate a species with large, at maturity dark brown, muriform spores (without hymenial algae) which showed an aberrant morphology: ascomata sitting on a thalline cushion extended to a “stalk”. The genus, which now includes 4 species, has been recently emended by Savić & Tibell (2008): features regarded as characteristic, such as a squamulose thallus, double-walled perithecia and dark muriform ascospores do not supply a basis for the recognition of Henrica, not even in combination, the genus being primarily based on genetic differences.
5) Sporodictyon - The analysis by Savić & al. (2008) revealed strongly supported groups within Sporodyction, a small genus of c. 5 species, which also is reasonably easy to characterise and recognise morphologically, as the perithecia are more or less covered by the thallus and not immersed. Sporodictyon-species grow on rocks, particularly by streams and on lakeshores, and among mosses. The northern species were treated by Savić & Tibell (2009).
6) Thelidium - This genus was usually considered as closely related to Polyblastia, but in the sporological tradition was characterised exclusively by having transverse septa, whereas Polyblastia also has longitudinal septa. The strongly supported ‘Thelidium-clade’ in the analysis by Savić & al. (2008) contains a mixture of species included into Polyblastia, Thelidium, Staurothele and Verrucaria, with a dramatic variability in spore septation and colour, and even the presence of some species with hymenial algae. Many nomenclatural changes are expected to occur in these genera in the next future. Currently c. 100 species, mostly described more than one century ago, are classified Polyblastia. Good descriptions and a key to the British species are in Orange (2013b).
Besides the taxonomic problems at genus level, the entire group of lichens treated in this key is very poorly studied, and species delimitation, which is often based on the old monograph by Zschacke (1934), is frequently problematic.


Breuss O. 2020 (2019). Key to the species of Agonimia (lichenised Ascomycota, Verrucariaceae). Österr. Z. Pilzk., 28: 69-74.
Gueidan C., Roux C., Lutzoni F. 2007. Using a multigene phylogenetic analysis to assess generic delineation and character evolution in Verrucariaceae (Verrucariales, Ascomycota). Mycol. Res., 111: 1145-1168.
Gueidan C., Savi S., Thüs H., Roux C., Keller Ch., Tibell L., Prieto M., Heiðmarsson S., Breuss O., Orange A., Fröberg L., Amtoft Wynns A., Navarro-Rosinés P., Krzewicka B., Pykälä J., Grube M., Lutzoni F. 2009. Generic classification of the Verrucariaceae (Ascomycota) based on molecular and morphological evidence: recent progress and remaining challenges. Taxon, 58, 1: 184-208.
Hafellner J. 2011. Halospora resurrected and segregated from Merismatium. Bibl. Lichenol., 106: 75-93.
Hafellner J. 2014. Distributional and other data for some Agonimia species (Verrucariales, lichenized Ascomycota). Fritschiana, 78: 25-46.
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.
Orange A. 2013. British and Other Pyrenocarpous Lichens. Vers. II. August 2013.
Pykälä J., Myllys L. 2016. Three new species of Atla from calcareous rocks (Verrucariaceae, lichenized Ascomycota). Lichenologist, 48, 2: 111-120.
Savić S., Tibell L. 2008. Atla, a new genus in the Verrucariaceae (Verrucariales). Lichenologist, 40, 4: 269-282.
Savić S., Tibell L. 2009. Taxonomy and species delimitation in Sporodyction (Verrucariaceae) in Northern Europe and the adjacent Arctic. Taxon, 58: 585-605.
Savić S., Tibell L., Gueidan C., Lutzoni F. 2008. Molecular phylogeny and systematics of Polyblastia (Verrucariaceae, Eurotiomycetes) and allied genera. Mycol. Res., 112: 1307-1318.
Zschacke H. 1934. Epigloeaceae, Verrucariaceae und Dermatocarpaceae. In: Dr. L. Rabenhorst‘s Kryptogamen-Flora, Band 9, Abt. 1, Teil 1. Akademische Verlagsgesellschaft, Leipzig, 695 pp.

Last modified: August, 29, 2023