Xanthoria parietina (L.) Th. Fr. s.l.
Thallus foliose, often forming extensive patches or rosettes, 5 to 15 cm diam., ± regular, made of flat or wrinkled lobes loosely appressed, 0,2-0,7 mm wide, upper surface smooth and without crystals, bright orange, yellow-orange, gold-orange in sunny locations but yellow-green in shaded areas (the lobe margins usually retain their yellow tinge), grey, grey-greenish, grey-glaucous in highly exposed areas; old specimen may have their center dying out or replaced by a new rosette-shaped thallus, attached by hapters. Apothecia usually numerous, sessile, 2 to 5 mm diam., disc flat to concave, orange to yellow orange if well exposed to sun or green in shaded locations, exciple persistent, paler, more or less crenulate and hardly visible on old humid specimen. Ascospores ellipsoid, with 2 poles at the top, 12-16 x 7-9 µm. Photobiont: trebouxioid. K+ purple. Very common and variable species, on a wide variety of nutrient-rich and enriched substrata, found everywhere, from rocks on the sea shore to inland or cities, including walls, wayside trees and roofing tiles. Up to now, taxonomy is still unclear and whether sea-shore specimen are different species, varieties, morphs is still pending but the preliminary molecular investigations seem to demonstate that several taxa would exist (additional investigations are awaited to clarify this issue) and usual morphological approaches are useless in that case. N.B. Near the sea shore some puzzling intermediate specimen between Xanthoria calcicola (that, due to its chemical composition, has no pale grey-greenish colours) and to a less extent some morphs of Xanthoria aureola may exist. On the small twigs and also but less frequently on cement, see Xanthoria polycarpa of which the thallus is less than 3 cm wide, apothecia are crowded, shortly stalked and cover almost all the thallus.
Here we present, on a provisional basis, different taxa based solely on morphological variations. To be revised in the light of additional molecular investigations.
Xanthoria parietina forme corticole. On bark of trees, notably in urban areas.
Xanthoria parietina forme isidiée. Green form restricted to North faces of trunks of deciduous trees, with isidioid excescences towards thallus center.
Xanthoria parietina forme lignicole des épaves en bois. On wood in the coastal zone and notably on painted wood ship wrecks and subjected to toxic compounds.
Xanthoria parietina forme saxicole des rochers acides de la zone xérique.
Xanthoria parietina forme saxicole des rochers alcalins de la zone mésique.
Xanthoria parietina forme lignicole sur bois travaillé. Common on street furnitures near the seashore.
Xanthoria parietina forme lignicole des poteaux en bois en milieu marin. Luxurious form, mainly thriving on wood poles and boards sticked into coastal mudflats.
Xanthoria parietina forme ramicole. Brightly colored form coming on the branches of trees and shrubs by the sea.