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Arthrorhaphis vacillans Th. Fr. & Almq. ex Th. Fr.
Family: Arthrorhaphidaceae
Arthrorhaphis vacillans image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus sulphur-yellow to whitish, the margins effigurate; the lobes to 2 mm broad, commonly less, verrucose, esorediate. Apothecia adnate, 0.5-0.7 mm broad, flat, black, epruinose; margin persistent, thin; disk minutely roughened; exciple green-black; hypothecium pale; epihymenium greenish blue; hymenium 90-110 µm, hyaline below, 1+ yellowish; paraphyses slender, coherent, tips not thickened; asci subcylindrical; spores straight, bifusiform, 3-septate (rarely 5-septate), 16-20 X 3-4 µm.

Reactions: K—, C —, P —.

Contents: rhizocarpic acid (Huneck & Follmann 1972).

This species is reported as growing over other lichens, particularly Baeomyces, and then becoming independent. It was described from Novaya Zemlya and is also known from Sweden, the Alps, Siberia, and northeastern Greenland. A species such as this, with so few records and seeming to be circumpolar, may occur in the American Arctic, although not yet collected there.