Abstract
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.