rose of Sharon, althea
蕣 refers to flowering plants in the mallow family, specifically the rose of Sharon (althea). The meaning is a specific botanical name rather than a broad conceptual idea.
蕣 combines the grass radical 艹 with 舜, which likely contributes the sound. The character is used for the rose of Sharon, a flowering plant.
The grass radical 艹 sits above 舜, like a flowering plant growing upward. Think of the rose of Sharon blooming from this grassy base.
For シュン, imagine a rose of Sharon blooming soon in the garden: soon -> シュン, and the flower opens quickly.