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Rhizocarpon ferax H. Magn.
Family: Rhizocarpaceae
[Rhizocarpon drepanodes Feuerer,  more]
Rhizocarpon ferax image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus areolate, the areolae to 1 mm broad, usually slightly crescent-shaped, more or less convex, greenish yellow to grayish yellow, smooth, dull; black hypothallus thin, usually present. Apothecia to 0.7 mm, round to roundish, more or less flat; margin thin, persistent; exciple brownish; hypothecium brownish; epithecium indistinct, greenish; hymenium 130-200 µm, hyaline to greenish, upper part brown to gree; paraphyses clavate, transparent; spores 8, with halo, muriform with many septa, dark, 25-40 X 14-18 µm.

Reactions: medulla K—, P+ yellow, 14-blue; exciple K+ brownish red; hypothecium K— or rarely K+ reddish; upper part of hymenium K— or K+ more green.

Contents: rhizocarpic acid and psoromic acid.

This species grows on calcareous rocks. It appears to be circumpolar arctic. It is similar to R. lecanorinum but has psoromic acid instead of stictic acid and has slightly less septate spores.