Verrucaria ahtii

The lichen was formally described as a new species in 2017 by Juha Pykälä, Annina Launis, and Leena Myllys. The type specimen was collected by the first author in Lohja (Southwest Finland) on a high road bank northwest of a lime processing factory; there it was found growing on a pebbles that may have been enriched by calcium-rich dust. The species epithet honours Finnish lichenologist Teuvo Ahti, "for his major contributions to lichenology".[1] The type specimen is kept in the collections of the mycological herbaria of the Botanical Museum of the Finnish Museum of Natural History.[2]

Molecular phylogenetic analysis of DNA sequences from the internal transcribed spacer regions shows that Verrucaria ahtii is closely related to V. vitikainenii.[1]

The crust-like thallus Verrucaria ahtii is usually from medium brown to dark grey (rarely, it is grey), and has a flake-like consistency. It has a medium- to dark-brown prothallus that is often inconspicuous. The perithecia are partly immersed in the thallus, measure 0.15–0.32 mm in diameter, and have a dark, flat, inconspicuous ostiole (pore). The exciple (the ring-shaped tissue layer surrounding the hymenium) measures 0.16–0.32 mm and has a dark brown wall about 13–18 μm thick. Algal cells are 5–11 μm wide. Ascospores are 20.6–25.5 by 10.2–12.4 μm and lack a perispore (a colorless, often gelatinous enveloping layer).[1]

Verrucaria ahtii grows on calcareous pebbles, and on siliceous pebbles that have been enriched with calcareous dust. It prefers sunny habitats, and has been recorded from south-facing rock walls in lime quarries. The lichen was originally known to occur in Finland, Lithuania, and Russia.[1] In 2018, it was recorded from Switzerland, where it was found growing on calcareous plaster on a humid and shaded wall.[3] The Lithuanian and Russian collections were incorrectly reported as Verrucaria invenusta.[1]

• List of Verrucaria species