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 without cilia or seldom scarce and short, lower surface blackish with scarce rhizines towards margins. 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 especially maritime but very common in our prospection area, on any type of substrata, frequent near the seashore on rocks, walls, tuft bases and also on well-lit trees. N.B. Not to be confused with some forms of Parmotrema reticulatum of which the reticulum of the lobe upper surface is limited, the soralia distribution suggest a pearl necklace and the lower surface of its margin is devoid of rhizines. If long black cilia are found at lobe margins and if Pd-, see Parmotrema arnoldii.

We can 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.