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Description

 Life habit: lichenized; Thallus: foliose, often circular in outline, ± loosely adnate, lobate; lobes: discrete or overlapping, short to elongate mostly < 3 mm wide, tips with or without cilia; upper surface: whitish gray or bluish gray to gray, dull or somewhat shiny, sometimes maculate or white pruinose; with or without soredia or isidia; upper cortex: paraplectenchymatous; medulla: white; photobiont: primary one a trebouxoid alga, secondary photobiont absent; lower cortex: proso- or paraplectenchymatous (lumina < 2.5 µm wide or 4-7 µm wide, respectively); lower surface: white, pale gray, pale tan or occasionally pinkish, sparsely to densely rhizinate; rhizines simple or furcate; Ascomata: apothecial, lecanorine, sessile or shortly stipitate: disc: brown to black, sometimes pruinose; epithecium: pale brown; hymenium and hypothecium colorless; paraphyses: simple or forked above, apices clavate, pale brown with a dark brown cap; asci: cylindrical, 8-spored, Lecanora-type; ascospores: brown, 1-septate, Physcia to Pachysporaria type, usually 15-25 µm long; Conidiomata: pycnidial, immersed, walls colorless except for a dark region around the ostiole; conidia: simple, subcylindrical, colorless; Secondary metabolites: cortex always with atranorin, medulla with or without atranorin, zeorin or other triterpenes; Geography: world-wide, found on all continents, particularly common in temperate regions; Substrate: common on bark, wood and rocks; less common on soil and artificial substrates.; Notes: Apart from the fact that most Physcias are substantially smaller than Heterodermias, a major difference is that the upper cortex of Physcia is always paraplectenchymatous whereas the upper cortex of Heterodermia is prosoplectenchymatous. In contrast, Phaeophyscia is similar in size to Physcia, but it never has atranorin in the upper cortex and hence reacts K-. 

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© Lichen Unlimited: Arizona State University, Tempe.

Source: Lichen Flora of the Greater Sonoran Desert Region

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