The genus Diploschistes, presently included either in the Graphidaceae or Diploschistaceae (Kraichak & al. 2018), comprises more than 30 species of crustose, saxicolous or terricolous lichens with a carbonised proper exciple with lateral paraphyses, and a chemistry dominated by orcinol depsides. A revision based on morphological, chemical, and molecular data was published by Fernández-Brime & al. (2013), who distinguished three lineages treated as distinct subgenera.
Some phylogenetic studies revealed the monophyly of Diploschistes, including D. ocellatus (e.g. Fernández-Brime & al. 2013), but others found that the genus, in its broad circumscription, is not monophyletic (e.g. Rivas Plata & al. 2013). Such discrepancies led Kraichak & al. (2013) to increase the numbers of molecular markers, showing that D. ocellatus is only distantly related to Diploschistes s.str. While taxa in Diploschistes s.str. have perithecioid to urceolate ascomata and a dark-pigmented, paraplectenchymatous exciple with lateral paraphyses, D. ocellatus has lecanoroid ascomata, a reduced exciple and lacks lateral paraphyses; chemically, it also differs in containing the norstictic acid chemosyndrome. Because of these differences the species, which was previously classified in subgen. Thorstenia within Diploschistes (Fernández-Brime & al. 2013), was included into Xalocoa, a new monotypic genus, by Kraichak & al. (2013).
Another monotypic genus, Ingvariella, was segregated from Diploschistes by Guderley & al. (1997), due to the absence of a true exciple, this being replaced by a pseudoexciple of degenerating, pigmented hymenial elements, and was originally placed within the Thelotremataceae (now often recognized as part of the Graphidaceae). However, the hymenium and amyloid ascus wall suggest different affinities. The phylogenetic study by Fernandez-Brime & al. (2011) demonstrated that Ingvariella is a member of the Stictidaceae, sister to the mainly saprotrophic genus Cryptodiscus.
The genus Diploschistes, in the traditional circumscription, was monographed, for species occurring in the Holarctic, by Lumbsch (1989).
Within D. scruposus, the following infraspecific taxa were distinguished by Clauzade & Roux (1985): 1) subsp. violarius (Nyl.) Clauzade & Cl. Roux, with an epruinose thallus reacting K+ bright yellow turning violet red-brown; 2) subsp. iridatus (A. Massal.) Clauzade & Cl. Roux, with an epruinose thallus reacting K-, on calciferous soil above treeline; 3) subsp. interpediens (Nyl.) Clauzade & Cl. Roux, with 8-spored asci and thallus K+ yellow then brownish, saxicolous. However, according to Fernández-Brime & al. (2013), molecular variability does not correlate with either morphological or chemical diversity, so that, pending further studies, we include these taxa into D. scruposus in a broad sense. The species delimitation in the D. scruposus group with urceolate ascomata requires further studies. As in other species complexes that diversified recently, multi-gene studies are insufficient to resolve independent lineages (Zhao & al. 2017).
The present key includes all species (incl. Xalocoa and Ingvariella) which are known to occur in Italy (see Nimis 2016), for a total of 10 infrageneric taxa.

References

Clauzade G., Roux C. 1985. Likenoj de Okcidenta Europo. Ilustrita determinlibro. Bull. Soc. Bot. Centre-Ouest, N. Ser., N. Spec. 7. Royan, 893 pp.
Fernández-Brime S., Llimona X., Molnar K., Stenroos S., Högnabba F., Björk C., Lutzoni F., Gaya E. 2011. Expansion of the Stictidaceae by the addition of the saxicolous lichen-forming genus Ingvariella. Mycologia, 103, 4: 755-763.
Fernández-Brime S., Llimona X., Lutzoni F., Gaya E. 2013. Phylogenetic study of Diploschistes (lichen-forming Ascomycota: Ostropales: Graphidaceae), based on morphological, chemical, and molecular data. Taxon, 62, 2: 267-280.
Guderley R., Lumbsch H.T., Feige B. 1997. Ingvariella, a new genus in the Thelotremataceae (lichenised Ascomycotina). Nova Hedwigia, 1-2: 147-154.
Kraichak E., Parnmen S., Lücking R., Lumbsch H.T. 2013. Gintarasia and Xalocoa, two new genera to accommodate temperate to subtropical species in the predominantly tropical Graphidaceae (Ostropales, Ascomycota) Austr. Syst. Bot., 26: 466-474.
Kraichak E., Huang J.P., Nelsen M., Leavitt S.D., Lumbsch H.T. 2018. A revised classification of orders and families in the two major subclasses of Lecanoromycetes (Ascomycota) based on a temporal approach. Bot. J. Linn. Soc., 188: 233-249.
Lumbsch H.T. 1989. Die holartischen Vertreter der Flechtengattung Diploschistes (Thelotremataceae). J. Hattori Bot. Lab., 66: 133-196.
Nimis P.L. 2016. The lichens of Italy. A second annotated catalogue. EUT, Trieste, 740 pp.
Rivas Plata E., Parnmen S., Staiger B., Mangold A., Frisch A., Weerakoon G., Hernandez J.E., Caceres M.E.S., Kalb K., Sipman H.J.M., Common R.S., Nelsen M.P., Lücking R., Lumbsch H.T. 2013. A molecular phylogeny of Graphidaceae (Ascomycota, Lecanoromycetes, Ostropales) including 428 species. MycoKeys, 6: 55-94.
Zhao X., Fernández-Brime S., Wedin M., Locke M., Leavitt S.D., Lumbsch H.T. 2017. Using multi-locus sequence data for addressing species boundaries in commonly accepted lichen-forming fungal species. Org. Div. Evol., 17: 351-363.

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