This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
艿 combines the grass radical 艹 with 乃, but the exact historical development and original meaning are uncertain.
The grass top 艹 suggests a plant, but the lower part 乃 does not give a clear meaning. Think of it as a mysterious plant whose name is unknown.
For ジョウ, imagine a gardener named Joe tending this unknown grass: Joe -> ジョウ, and he cares for the mysterious plant.
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