The tiny spores of ferns, historically believed to be invisible or magical seeds that grew in darkness or granted invisibility.
Compound of 'fern' and 'seed,' from medieval and early modern folklore. Ferns actually reproduce by microscopic spores, not visible seeds.
Medieval people believed fernseed was invisible and could make you invisible too—this magical belief persisted because fern spores are actually too tiny to see without a microscope!
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