Evernia prunastri

Oakmoss is not actually a moss but a lichen, which is a symbiosis between fungi and photosynthetic organisms (often algae). Eventhough they often look like plants, lichen are not considered plants. This lichen can be found throughout most of the northern hemisphere, where it lives on the trunk and branches of deciduous trees (primarily oak trees) and conifers, and occasionally also on walls. It likes wet, well vented and bright habitats and suffers from pollution, which is why it is endangered even critically endangered in some parts.

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