This is a key to all crustose pyrenocarpous lichens (Verrucariaceae and Thrombiaceae) with a green, non-Trentepohlioid photobiont and 1-celled ascospores known to occur in Italy (Nimis 2016), plus several species reported from the Alps outside Italian territory (Nimis & al. 2018) for a total of 170 infrageneric taxa. Many poorly known species of Verrucaria were described from Italy, especially by Servít; most of them (those which have not been re-evaluated in recent papers) were listed separately under the poorly known taxa by Nimis (2016), and are not included in the key.
The taxonomy of the Verrucariaceae is presently being thoroughly revised on the basis of molecular data (see e.g. Gueidan & al. 2007, 2009). 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 characterizing natural groups, so that these genera, as currently delimited, are non-monophyletic.
This key, besides crustose species of Heteroplacidium and Involucropyrenium, includes the following genera:
1) Bagliettoa A. Massal. This genus accommodates a group of species formerly treated as members of Verrucaria, which are characterised by a radially sulcate involucrellum (missing in some species), immersed perithecia, and an endolithic thallus with a lithocortex, that occur on limestone or on dolomite, and have a mainly southern distribution in Europe. The group has been extensively treated by Halda (2003), who does not recognise it as worthy of being treated at generic rank and accepts a few species only. A molecular study by Gueidan & al. (2007) has, however, demonstrated that the species included in Bagliettoa are indeed closely related, forming a well-defined lineage within the Verrucariaceae. The molecular study by Yuzon & al. (2013), which we mainly follow here, confirms that the genus is well-founded and recognizes 12 species.
2) Hydopunctaria C. Keller, Gueidan & Thüs - This recently-described genus includes mainly amphibious species with small to medium sized ascospores and the frequent formation of carbonaceous structures with a punctiform to column-like appearance in the thallus. The genus is still very poorly known in Italy, and there is evidence that, both in marine (e.g. see Orange 2012, 2013a) and in freshwater species (e.g. see Thüss & al. 2915) several semi-cryptic species still await to be discovered.
3) Parabagliettoa Gueidan & Cl. Roux - According to Gueidan & al. (2009) Parabagliettoa is sister to Bagliettoa, differing mainly by the thallus having a pseudocortex (in opposition to the well differentiated lithocortex in Bagliettoa), and superficial perithecia with an involucrellum that is not radially split. The genus includes so far 3 species only, all of which do occur in Italy, but several species of Verrucaria will be likely added to the genus in the future.
4) Placocarpus Gueidan & Cl. Roux -This small genus, which includes 3 species only, is a sister genus to Verrucula (Gueidan & al. 2007), which includes only species parasitic on Teloschistaceae with anthraquinones. Two of the known species are juvenile parasites on species of Protoparmeliopsis.
5) Placopyrenium Breuss - This genus was established by Breuss (1987) to include species formerly placed in Dermatocarpon with placodioid thalli and areoles fixed to the substrate by stipe-like holdfasts. The circumscription of the genus has been subsequently enlarged to include species without black-rimmed areoles as well as lichenicolous ones, formerly treated as Dermatocarpon and Catapyrenium (see Breuss 2009) plus two members of the Verrucaria fuscella- group (Navarro-Rosines & al. 2007). Currently the genus contains c. 22 species characterised by an areolate to subsquamulose thallus, immersed perithecia with a reduced or missing involucrellum, colourless, simple or 1-(-2)-septate ascospores, and pycnidia of the Dermatocarpon-type. A general key was published by Breuss (2009). For further details see also Gueidan & al. (2009) and Orange (2013b). A species described from Italy, which probably belongs to this genus, is Dermatocarpon gorzegnoense Servít, which is known only from the type material (Piedmont), and needs further study.
6) Thrombium Wallr. - This genus of the Thrombiaceae is distinguished from other pyrenocarpous lichens by the combination of: lack of involucrellum, colourless, simple ascospores and persistent paraphyses. Similarities in ascus structure and molecular data suggest a close relationship of the Thrombiaceae with Protothelenella in the Protothelenellaceae, a family of uncertain taxonomic position (Schmitt & al. 2005).
7) Verrucaria Schrad. - A large, very heterogeneous genus of several hundreds species, one of the most poorly known genera of the European flora. Numerous species were previously described from Europe, several of them even in recent years (e.g. see Orange 2004, 2013a, 2014; Aptroot & Thüs 2011; Breuss & Berger 2012; Thüs et al. 2015, 2018; Pykälä & al. 2017a, b, 2018, 2019), but the species concepts are largely based on a few morphological characters only, and species delimitation was not always confirmed by the few available molecular studies.
8) Verrucula J. Steiner - This genus of the Verrucariaceae was segregated from Verrucaria to accommodate a group of species which are mainly parasitic on species of Caloplaca s.lat. with anthraquinones, and on Rusavskia elegans. The genus is closely related to Placocarpus. In Verrucula, specificity to the lichen host seems to be high, since in general each host species is colonised by a different species of Verrucula (Navarro-Rosinés & al. 2007), leading to the current recognition of 30 species. However, it has also been suggested that, because of the low morphological variation in this group, all species parasitic on the species of the former Caloplaca section Gasparrinia could in fact constitute a single species. For further details see Navarro-Rosinés & al. (2007) and Gueidan & al. (2009).
9) Verruculopsis Gueidan, Nav.-Ros. & Cl. Roux - This genus of the Verrucariaceae, with c. 4 species, was initially created to segregate from Verrucaria a group of mainly parasitic species which are related to Placopyrenium. Species of both Verrucula and Verruculopsis are morphologically quite similar, probably as a result of a convergence to parasitism. Only a few characters help in distinguishing them: in Verrucula, the exciple is pale except for the part around the ostiole, whereas in Verruculopsis the exciple is, at maturity, pale brown at base and dark brown in the upper part. Moreover, the medulla in Verrucula is I+(blue) to I-, whereas Verruculopsis has always a I- medulla. The concept of the genus has been later enlarged to include also V. lecideoides and V. minuta, which are morphologically quite different and do not grow on species of Teloschistaceae. For further details see Navarro-Rosinés & al. (2007) and Gueidan & al. (2009).
Important keys to the lichens treated here are those of Clauzade & Roux (1985) for Western Europe, Krzewicka,(2012) for Poland, Orange (2013b) for the British Isles, and Wirth & al. (2013) for Germany. Breuss & Berger (2010) produced an important key to calcicolous Verrucaria-species with a brown thallus in the Alps, while Pykälä & al. (2020) published a key to Verrucaria species with large spores, perithecia leaving pits in the rock and a pale thin thallus in Finland.
Due to the poor state of knowledge concerning the whole group, the present key should be considered as a provisional draft, which is being published online mainly for testing and gathering critical feedback by users.

References

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Last modified: March, 4, 2024

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