A genus of lichens commonly called Iceland moss, used historically for food, medicine, and textile dyes.
The origin is uncertain; possibly named after Cetraria as a place, or from a Scandinavian root. It became widely used in Nordic countries where the lichen grows abundantly on rocks and tundra.
Iceland moss isn't actually a moss at all—it's a lichen, which is a symbiotic partnership between a fungus and an alga, and Vikings actually ate it as an emergency food source!
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