Like all lichens are formed by the intimate symbiotic union between an alga and a fungus. The alga or phycobiont brings energy from photosynthesis, while the fungus or mycobiont provides water and minerals. Many millions of years ago learned to live together, helping each other, allowing them to successfully colonize the new land emerging from volcanic eruptions and tectonic plate movements. In fact, lichens are often the first living organisms to colonize the volcanic islands just after the lava cooled.
Young Xanthoria parietina on the bark of Acer negundo a greenish color to grow in the shade of the bark of maple with a lot of humidity.
This lichen was used in ancient pharmacopoeia for treating malaria with the name of lichen parietinus as a substitute for cinchona bark. It was also used as a dye for dyeing yellow and brown because it contains parietina.