A botanical classification grouping together all plants that reproduce by spores rather than visible flowers and seeds.
From 'crypto-' (hidden) + 'gamia' (from Greek 'gamos' meaning union). This was the formal Linnaean taxonomic class for non-flowering plants established in the 18th century.
Carl Linnaeus literally divided all plants into 'Phanerogamia' (flowering plants with obvious reproduction) and 'Cryptogamia' (hidden reproducers)—it seems so obvious now but was revolutionary when most people couldn't see spores!
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