This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The historical origin of 茮 is uncertain. It visually contains 艹 (grass) and 尗, but the exact development is unclear.
With no clear meaning, picture a mysterious plant (艹) with a small, bean-like seed (尗) — its purpose is unknown.
For ショウ, imagine showing (ショウ) this unknown plant to a botanist, hoping they can identify it.