Common Orange Lichen

The common orange lichen (Xanthoria parietina) forms bright orange to yellow crusts on walls, roofs, rocks and tree bark across Europe and beyond. A lichen is not one organism but a partnership between a fungus and a photosynthetic partner.

🧬 Field Guide Specimen: Open Common Orange Lichen in the CRV Science Field Guide to log the specimen, see its place among the Opisthokonta lineages in the Cladogram Explorer, and test your recall in the Red List conservation game.

The fungus provides the structure, and green algae (here of the genus Trebouxia) living inside make sugars by photosynthesis. Together they can colonize bare surfaces where neither could live alone. Lichens reproduce by spores, and also by fragments containing both partners.

The orange color comes from parietin, a pigment that absorbs ultraviolet and blue light and protects the algae from strong sunlight. The lichen is more intensely colored in sunny spots.

Unlike most lichens, Xanthoria thrives where nitrogen is abundant, such as near bird perches, farmland and roadsides, and its spread can signal ammonia pollution. Many other lichens are sensitive to sulfur dioxide and decline in polluted air.