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 Thallus: foliose, up to 4 cm in diam., irregular to more often orbicular; lobes: elongate and discrete to somewhat irregularly rounded and partly imbricate, 0.5-1(-1.5) mm broad, usually +flat, prostrate; upper surface: pale gray to dark gray or pale brown, epruinose and without distinctive epinecral layer, sorediate; soredia: powdery to finely granular, only rarely granular and pseudocorticate, in primarily laminal or submarginal soralia which are round to irregular; upper cortex: paraplectenchymatous; medulla: white; lower cortex: paraplectenchymatous; lower surface: black, sometimes paler at the lobe ends, dull or rather shiny; rhizines: simple, black; Apothecia: infrequent, up to 1.5 mm in diam., sessile, the margin entire or grossly crenate, usually with a corona of rhizines; ascospores: narrowly ellipsoid, 19-25(-28) x 7.5-11 µm, Physcia-type; Spot tests: all negative in cortex and medulla; Secondary metabolites: none detected.; Substrate and ecology: usually on bark, occasional on rock; World distribution: North America (primarily western), Europe; Sonoran distribution: mountains of southern California and Arizona.; Notes: Three rare or infrequent species, Phaeophyscia adiastola, P. insignis,, and P. pusilloides, must be carefully distinguished (see notes for each of them), but the common species in the study area which has been most commonly confused with P. orbicularis is P. hispidula. Most specimens of P. hispidula are distinctly larger and broader lobed, but some corticolous forms can easily overlap in size with P. orbicularis. Many of these corticolous forms of P. hispidula have laminal, granular soredia not too different from those of P. orbicularis, and they can be distinguished by the distinctive concave/upturned lobes, and the longer, more conspicuous rhizines visible from above at lobe edges, at least a few of which are on the margin and pointing distinctly upward. 

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© Lichen Unlimited: Arizona State University, Tempe.

Source: Lichen Flora of the Greater Sonoran Desert Region

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