A taxonomic group of flowering plants lacking a perianth; an outdated botanical classification.
From Latin 'achlamydeus' (without a cloak) + plural suffix '-ae'. Used in 19th-20th century botanical classification before modern phylogenetic systems replaced it.
This classification system is now considered obsolete because achlamydate flowers are scattered across unrelated plant families—scientists learned that lacking petals tells you nothing about actual evolutionary relationships!
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