kind of wild ginger
蘘 refers to a specific kind of wild ginger plant. Its meaning is narrow and botanical, without broader abstract extensions.
蘘 combines the grass radical 艹 with the phonetic component 襄, which likely contributed the sound. The character was created to name a specific plant.
The grass radical 艹 sits above 襄, like a wild ginger plant growing up from a dense cluster of leaves and roots.
For ニョウ, imagine a wild ginger plant growing in New York: New -> ニョウ, and the plant thrives in an urban garden.