Taxonomy of Thelidiumauruntii and T.incavatum complexes (lichenized Ascomycota, Verrucariales) in Finland.

The taxonomy of lichen species morphologically similar to Thelidiumauruntii and T.incavatum in Finland is being revised. Based on ITS and morphology, ten species occur in Finland. All species are restricted to calcareous rocks. The Thelidiumauruntii morphocomplex includes six species: T.auruntii, T.huuskoneniisp. nov., T.pseudoauruntiisp. nov., T.sallaense sp. nov, T.toskalharjiensesp. nov. and T. sp. 1. In the ITS phylogeny, T.auruntii, T.pseudoauruntii and T.sallaense group together, but the remaining species are placed outside of this clade. All the species have northern distribution in Finland, occurring on fells in NW Finland and/or in gorges in the Oulanka area in NE Finland. The Thelidiumincavatum morphocomplex includes four species: T.declivumsp. nov., T.incavatum, T.mendaxsp. nov. and T. sp. 2. This morphogroup is not resolved as monophyletic in the ITS phylogeny, with only T.declivum and T.mendax forming a strongly supported group. Thelidiumincavatum is rather common in SW Finland, with one separate locality in eastern Finland. Thelidiumdeclivum occurs only in the Oulanka area. Thelidiummendax occurs in the Oulanka area, but one locality is known from eastern central Finland. Thelidium sp. 2 is known from one locality in SW Lapland.

Lichen speciation is sparked by a substrate requirement shift and reproduction mode differentiation.

We show that obligate lignicoles in lichenized Micarea are predominately asexual whereas most facultative lignicoles reproduce sexually. Our phylogenetic analyses (ITS, mtSSU, Mcm7) together with ancestral state reconstruction show that the shift in reproduction mode has evolved independently several times within the group and that facultative and obligate lignicoles are sister species. The analyses support the assumption that the ancestor of these species was a facultative lignicole. We hypothezise that a shift in substrate requirement from bark to wood leads to differentiation in reproduction mode and becomes a driver of speciation. This is the first example of lichenized fungi where reproduction mode is connected to substrate requirement. This is also the first example where such an association is demonstrated to spark lichen speciation. Our main hypothesis is that obligate species on dead wood need to colonize new suitable substrata relatively fast and asexual reproduction is more effective a strategy for successful colonization.

Corrigendum: Pykälä J, Kantelinen A, Myllys L (2020) Taxonomy of Verrucaria species characterised by large spores, perithecia leaving pits in the rock and a pale thin thallus in Finland. MycoKeys 72: 43-92. https://doi.org/10.3897/mycokeys.72.56223.

[This corrects the article DOI: 10.3897/mycokeys.72.56223.].

Taxonomy of Verrucaria species characterised by large spores, perithecia leaving pits in the rock and a pale thin thallus in Finland.

Species of Verrucaria, characterised by large spores (at least some spores exceeding 25 µm in length), perithecia leaving pits in the rock and a pale thin thallus, form a taxonomically-difficult and poorly-known group. In this study, such species occurring in Finland are revised, based on ITS sequences and morphology. Maximum likelihood analysis of ITS sequence data was used to examine if the species belong to the Thelidium group, as suggested by BLAST search. Twelve species are accepted in Finland: Verrucaria bifurcata sp. nov., V. cavernarum sp. nov., V. devergens, V. difficilis sp. nov., V. foveolata, V. fuscozonata sp. nov., V. karelica, V. kuusamoensis sp. nov., V. subdevergens sp. nov., V. subjunctiva, V. subtilis and V. vacillans sp. nov. Verrucaria foveolata is nested in V. subjunctiva in the phylogeny, but due to morphological and ecogeographical differences, the two taxa are treated as separate species pending further studies. Based on the analysis, the study species belong to the Thelidium group. The studied species show a rather high infraspecific morphological, but a low genetic variation. Furthermore, they show considerable overlap in their morphology and many specimens cannot be reliably identified, based on morphology only. All species are restricted to calcareous rocks. Verrucaria alpigena, V. cinereorufa and V. hochstetteri are excluded from the lichen flora of Finland. Verrucaria grossa is considered a species with unresolved identity. Verrucaria foveolata and V. subtilis are rather common on calcareous rocks of Finland while V. devergens and V. kuusamoensis are restricted to northern Finland. Verrucaria subjunctiva occurs mainly in northern Finland. Verrucaria bifurcata has been found only from southern Finland. Verrucaria difficilis has few localities both in SW and NE Finland. Verrucaria vacillans is restricted to calcareous rocks (dolomite) on the mountains of the NW corner of Finland. Verrucaria fuscozonata, V. karelica and V. subdevergens occur only in the Oulanka area in NE Finland. A lectotype is designated for V. subjunctiva. The morphology of the Finnish species was compared with 51 European species of Verrucaria presumably belonging to the Thelidium group.