Physcia dubia (Hoffm.) Lettau var. dubia
Physcia caesia var. dubia (Hoffm.) Th. Fr.
Thallus foliose, rosette-shaped, 3-5 cm diam., tightly appressed to the substratum, lobes radiating with palmate extremities, 0.5-1 mm wide, not separated from each others, upper surface grey, pale grey when dry, grey-glaucous or greeenish when moist, without pseudocyphella, sometimes -but seldom- faintly whitish flecked, lobe ends characterized with small greyish, or grey-yellowish when moist, small soralia heaps, lip-shaped, potentially spreading all over the thallus center; lower surface whtish, with rather sparse, whitish to brown, mostly simple rhizines. Apothecia very rare, 1-2 mm diam., thalline exciple sorediate. Ascospores brown, broadly ellipsoid, 1-septate, 16-25 x 7-11 µm. Cortex : K+ yellow ; medulla : K-. Rather rare, on nutrient-rich substrata, on dusty or dull acid rocks, sometimes on trunks and wood. N.B. Resembles to Physcia tenella but devoid of cilia, and to Physcia caesia that has distinct pseudocyphella, K+ yellow medulla and grey-bluish soredia.
N.B. A very misleading and variously interpreted species which has only recently been separated from Physcia tribacia with more globular and more numerous soralia and which occurs mainly on the bark. This last very variable species is also very often difficult to separate in the field by its macroscopic characters and requires a microscopic examination (lower paraplectenchymal cortex). See Physcia dubia var. teretiuscula whose lobes are very elongated and separated from each other and which is mountainous.