This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
莭 is a rare character whose exact historical development is uncertain. It visually combines 艹 (grass) with 即, but the original semantic and phonetic roles are unclear.
The top grass radical 艹 and the bottom 即 suggest a plant-related idea, but without a clear meaning, picture a mysterious herb that defies easy description.
For セツ, imagine a set of rare herbs: set -> セツ, and the grass radical 艹 hints at the plant connection.