This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 茛 is uncertain. It visually combines the grass radical 艹 with 艮, but the original semantic and phonetic roles are unclear.
With no clear meaning, picture the grass radical 艹 covering the bottom shape 艮 like a mysterious plant whose name is lost.
For コン, imagine a con artist hiding a rare plant under the grass: con -> コン, and the plant's identity is a mystery.