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Verrucaria deversa Vainio
Family: Verrucariaceae
Verrucaria deversa image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.

Thallus thin, immersed in the rock, whitish, lacking any bordering line.

Perithecia with the base immersed in the rock or up to half immersed, hemispherical, 0.25-0.3 mm broad, black, bare; aperture of ostiole not prominent or becoming depressed as an ostiolar cavity; exciple nearly globose, brown or reddish brown, entire, evenly thickened or with the upper part thicker; gelatin I+ reddish or rarely bluish; spores ellipsoid oblong, 15-25 X 7-10 µm.

This species grows on calcareous rocks.  It is apparently circumpolar arctic, being known from northern Europe, Siberia, Greenland, and the American Arctic.