Physconia grisea (Lam.) Poelt subsp. grisea

    Thallus foliose, more or less rosette-shaped, 5-8 cm diam., tightly appressed to the substratum, composed of lobes, 1-2 mm wide, radiating and partly overlapping, upper surface markedly spotted pruinose, whitish, conspicuous towards the margins, spots possibly contiguous in the center, overall aspect pale greyish, pale grey-brownish when dry, bronze to brown-greenish when moist, markedly green when rainy or rehydrated, covered notably towards the center with granular isidia and sorelia, grey-greeenish, lower surface whitish, darker in the center, simple rhizines, whitish to pale ochre. Apothecia very rare, more or less sessile, 1-3 mm diam., disc brown-red, pruinose, thalline exciple sorediate. Ascospores brown, thick walls, minutely dotted, 22-34 x 12-17 µm. Pycnidia frequent. Cortex: K-; medulla (white): K-. On nutrient-enriched bark of deciduous tree trunks in parklands or isolate, also on rocks and walls provided that the substratum is neutral or alkaline, sometimes on the peeled trunks of dead trees and even on wood, see: Physconia grisea forme lignicole

N.B. Not to be confused with Physconia perisidiosa a of which the rhizines are bottle-brush-shaped and with  Physconia enteroxantha which has a yellow medulla K+ yellow.

N.B. There is a thermophilic form from the Islands or the Atlantic coasts with a purplish-grey color in dry weather and glaucous-grey in wet weather, see: Physconia grisea subsp. grisea forme thermophile Atlantique.