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Yellow Scales

Yellow Scales - WWC Archives

Xanthoria parietina is a foliose, or leafy, lichen. It has wide distribution, and many common names such as common orange lichen, yellow scale, maritime sunburst lichen and shore lichen. It can be found near the shore on rocks or walls and also on inland rocks, walls, or tree bark.


The vegetative body of the lichen, the thallus, is foliose, and typically less than 8 centimetres (3.1 in) wide. The lobes of the thallus are 1–4 mm in diameter, and flattened down. The upper surface is some shade of yellow, orange, or greenish yellow, while the lower surface is white, with a cortex, and with sparse pale rhizines or hapters. The vegetative reproductive structures soredia and isidiaare absent in this species, however, apothecia are usually present.

The outer "skin" of the lichen, the cortex, is composed of closely packed fungal hyphae and serves to protect the thallus from water loss due to evaporation as well as harmful effects of high levels of irradiation. In Xanthoria parietina, the thickness of the thalli is known to vary depending on the habitat is which it grows. Thalli are much thinner in shady locations than in those exposed to full sunshine; this has the effect of protecting the algae that cannot tolerate high light intensities. The lichen pigment parietin gives this species a deep yellow or orange-red color.

Habitat and distribution[]

Hardwood forests in low-elevation broad valleys; scattered on Populus and other hardwoods in riparian areas in agricultural and populated areas. It is often associated with high level of nitrogen and favored by eutrophication and can be often found near farmland and around livestock.

Pollution tolerance[]

Xanthoria parietina is a very pollution-tolerant species. In laboratory experiments, this species can tolerate exposure to air contaminants and bisulphite ions with little or no damaging effect. It is also tolerant of heavy metal contamination.

For these reasons, this species has found use as a biomonitor for measuring levels of toxic elements.