Parmotrema perlatum (Huds.) M. Choisy

    Thallus foliose, rosette-forming, more or less regular, to 15 cm diam., lobes to 1-1.5 cm wide, smooth towards margins, wrinkled towards the center, margins wavy, indented, covered with a rim of continuous globose soralia (as a hem or a pearl necklace), slightly upturned (but some lobe margin sections are free of soralia), upper surface typically grey-pearly when dry and grey-greenish when moist, margin with more or less abundant black cilia depending on the forms, lower face black with simple, black rhizines, but the margin is brownish and without rhizines. Apothecia rare, disc brownish, exciple sorediate. Ascospores simple with thick walls, 21-28 x 13-15 µm. Cortex: K+ yellow; medulla : C-, K+ golden yellow, KC+ yellow-orange, Pd+ yellow-orange, red-orange. Not a particularly maritime species but very common in our prospecting area, occurring on all sorts of substrata but very frequent on the seaside.

N.B. To be distinguished from certain forms of Parmotrema reticulatum with a slightly reticulated upper surface of the lobes, by its "pearl necklace" soralia and by the margin of the lower surface of the lobes devoid of rhizines.

N.B. If long black cilia are found at lobe margins and if Pd-, see Parmotrema arnoldii. 

_ Very variable species and it is possible to observe different forms depending on the substrate:

Parmotrema perlatum forme corticole. Form occurring on the bark of trunks or large branches of trees.

Parmotrema perlatum forme saxicole. Form occuring on the rocks, the stones of the walls.

Parmotrema perlatum forme lignicole. Form occuring on bare wood.

Parmotrema perlatum forme ramicole. Small form, growing on small branches of trees.

Parmotrema perlatum forme sur substrat artificiel. Forme sans soralies marginales, ou alors très rares, et avec des cils marginaux très abondants.