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Arthonia mediella Nyl.
Family: Arthoniaceae
[Opegrapha mediella (Nyl.) M. Choisy]
Arthonia mediella image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus on bark, thin, continuous or chinkv. sometimes scaling from the substratum, smooth or roughened, yellowish, slightly shining. K—; margins indistinct and lacking black border lines.

Ascocarps dispersed. Lecidea-like, to 0.5 mm broad, lacking margin, the base constricted, flat to slightly convex, black, dull, epruinose; hypothecium brownish black; epithe-cium brownish black; hymenium 50-60 /xm. hyaline to yellowish, not inspersed, K-, 1+ orange-yellow; paraphyses moderately branched, thin, slightly capitate; asci clavate; spores elongate, spindle-shaped, straight, hyaline, 3-septate with equal-sized cells, 11-18 x 3-4/xm.Coni-dia 5-6 x 1 /im.

This spccics grows on a variety of woody plants, including Pinus. Picea, Alnus, and Quercus. and also on old wood. It appears to be circumpolar arctic-alpine and boreal, but it is rarely collected in North America, the only report being from Port Clarence. Alaska, by Nylandcr (1887 (1888)). It was collected by Vahl at Ikkatok, Greenland, and named by Theodore Fries as A. trabinrlla.