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Verrucaria rupestris Schrader
Family: Verrucariaceae
Verrucaria rupestris image
Lucy Taylor  
Thompson, J., 1984. American Arctic Lichens: The Macrolichens.
Thallus immersed, forming an ashy white discoloration on the rock; hypothallus lacking. Perithecia immersed in the rock with only the tip showing, 0.4 mm broad; cavities are left in the substratum when the perithecia fall out; exciple pale; involucrellum black, the upper part thick, thinning toward the base and wrapping around the exciple; gelatin 1+ blue turning reddish; spores ellipsoid-oblong, 17-23 X 9-13 µm.

This species is found on calcareous rocks in the open. It is a circumpolar species of wide distribution from the arctic to the temperate zones. In North America it ranges south to New England, Colorado, and California.