This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 蕻 is uncertain. It visually contains 艹 (grass), 镸 (long), and 共 (together), but the original semantic and phonetic roles of these components are unclear.
With no clear meaning, picture a rare plant (艹) that grows long (镸) and together (共) with others, but its purpose remains a mystery.
For コウ, imagine a rare plant named Kou that grows long and together with others: Kou -> コウ.