Parmotrema arnoldii (Du Rietz) Hale

    Thallus foliose, loosely attached to the substratum, to 5-20 cm across, lobes more or less imbricate, 0.5-1.5 cm wide, tips more or less indented and rounded, upper surface smooth, sometimes slightly maculate, grey-whitish when dry, pale grey-glaucous when moist, sometimes with small spots or some small grey-blackish sections (parasite signature?), margins with scarce soredia, in straight chain, pale grey-yellow and above all with cilia, 5 mm long or more, undulate or winding, black (not to be confused with simple rhizines from lower surface as frequently observed in other species); lower surface blackish to brownish with rhizines, scattered and simple. Apothecia very scarce, markedly sessile or sub-stipitate, 0.5-1 cm diam., disc concave, brown-orange, exciple concolourous to the thallus, crenulate. Ascospores simple, colourless, broadly ellipsoid, 15-22 x 9,5-12 µm. Photobiont: Trebouxioid. Cortex: K+ yellow; medulla: C-, K-, KC+ pink, Pd-. Thermophilic, strong oceanic trends, on main branches and trunks of deciduous trees, but also on slightly acid mossy rocks near the seashore. Rather similar to Parmotrema perlatum but differing by its long marginal black cilia, and the Pd- medulla reaction. Also close to Parmotrema reticulatum which is Pd+ red-orange and with lobe surfaces distinctly reticulated.*