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Verrucaria arctica Lynge
Family: Verrucariaceae
Verrucaria arctica image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus thin to moderately thick, areolate, the areolae small, convex to verrucose, smooth, dispersed to forming a more continuous verrucose-areolate crust, dark brown to ashy black. Perithecia globose, 0.25-0.4 mm broad, projecting from the areolae, the ostioles only slightly impressed; exciple entire, dark; involucrellum over part to two-thirds of the perithe-cium, dark; gelatin 1+ red; asci partly subcylin-drical and the spores then uniseriate; spores broadly ellipsoid to nearly globose, 8-14 x 6-10 µm.

This species grows on calcareous rocks. It is circumpolar arctic, known from Novaya Zemlya, northern Europe, Greenland, and northern North America. Material which I reported as V. obnigrescens from Alaska (Thomson 1979) is closer to this species.