This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 蒪 is uncertain. It visually contains 艹 (grass) and 尃, but the original meaning and component function are unclear.
The top 艹 suggests a plant, and the bottom 尃 is a rare shape. Picture an obscure plant whose name is lost, growing in an old garden.
For ハク, imagine a botanist named Haku discovering this mysterious plant: Haku -> ハク, and he carefully labels it with the grass radical 艹.
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