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 bifurcatasp. nov., V. cavernarumsp. nov., V. devergens, V. difficilissp. nov., V. foveolata, V. fuscozonatasp. nov., V. karelica, V. kuusamoensissp. nov., V. subdevergenssp. nov., V. subjunctiva, V. subtilis and V. vacillanssp. 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.