This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蒩 combines the grass radical 艹 with 租, but the exact historical development and original meaning are uncertain.
With no clear meaning, picture a rare plant (艹) whose name sounds like 租 (ソ), but its use is forgotten.
For ソ, imagine a single blade of grass (艹) that looks like the katakana ソ: the shape of the grass itself cues the reading.
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