type of plant
萇 refers to a type of plant. The given meaning is a broad botanical label without a clear conceptual center beyond its plant identity.
萇 combines the plant radical 艹 with 長, which likely contributes a phonetic element. The exact historical development is uncertain.
The top 艹 marks it as a plant, and the bottom 長 suggests something long. Picture a plant with unusually long leaves or stems: 萇 is that long plant.
For チョウ, imagine a long plant named Chou growing in a garden: Chou -> チョウ, and its long leaves stretch out.
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