This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 蓻 is uncertain. It visually combines 艹 (grass) with 執, but the original semantic and phonetic roles are unclear.
The top 艹 suggests grass, and the bottom 執 looks like a hand holding something. Without a clear meaning, you might imagine a rare plant being grasped.
For シュウ, imagine a rare grass that makes a soft 'shuu' sound when the wind blows through it: shuu -> シュウ.
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