Polyozosia albescens (Hoffm.) S.Y. Kondr., Lökös & Farkas morpho albescens. = Myriolecis albescens (Hoffm.) Sliwa, Zhao Xin & Lumbsch

   Thallus crustose rather thick, compact, 2-3 cm in diameter or larger and formed of smaller but neighboring thalli, the margin of the thalli is cracked and sometimes gives the impression of being lobed at the margin, cracked to areolate, areoles a little rounded or swollen, more or less pruinose, chalky white, dirty white. Lecanorine apothecia very numerous in compact groups on the thallus which they can cover entirely, more or less sessile and protruding but sometimes, especially at the beginning, a little immersed in the thallus, 0.5-2 mm, flat disc, sometimes a little convex if old or concave if humid, pale brown, light brown, yellowish brown, etc. sometimes a little pruinose. Margin very visible, erect, sinuous to a little crenate, white or concolorous to the thallus, containing large crystals or granules insoluble in KOH. Hymenium colorless, purple-brown in NO3H. Epithecium NO3H- without blue-green colorations. Asci utriform, 45-50 x 15-20 µm according to our measurements. Spores simple, broadly elliptical, 8-15 x 4-6 µm according to the literature, 9-12 x 4-5 according to our measurements. Photobiont: Trebouxia. C-, K-, KC-, P- but sometimes P+ apothecia margin orange, UV- or sometimes apothecia UV+ green. A highly variable species depending on its substrate and habitat, it probably contains several taxa. It is highly nitrophilous and resistant to pollution. It is not specifically marine, but it appears to contain marine taxa. It most often grows on sunny limestone or slightly acidic rocks, but also on old walls, concrete, and particularly on old blockhaus along the seashore. It is sometimes found on fiber cement. It is more rare on bark, wood, and artificial substrates.

N.B. It is easily confused with Polyozosia (Myriolecis, Lecanora) dispersa, which has a smaller, grayish or blackish thallus and more dispersed apothecia. It is also easily confused with Polyozosia (Myriolecis, Lecanora) bandolensis, a thermophilic marine species growing on limestone rocks, a much rarer species whose apothecia discs are heavily stained with a more or less dark blue-green.

N.B. Apothecia are sometimes parasitized by Arthonia apotheciorum, which then turns black.

Here we present some remarkable forms:

_ Polyozosia (Myriolecis, Lecanora) albescens forme lignicole, a wood-forming form that grows on worked wood along the seashore, particularly on wooden boat wrecks.

_ Polyozosia (Myriolecis (Lecanora) albescens forme corticole, a corticolous form that grows on tree bark, particularly street trees in urban areas in polluted areas.

_ Polyozosia (Myriolecis, Lecanora) albescens forme sur béton, a concrete-forming form that grows on the concrete of harbor structures and also on old blockhaus.