luxuriance of growth
菀 centers on lush, thriving plant growth: a scene of vegetation flourishing in abundance.
菀 combines the grass radical 艹 with 宛, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with lush vegetation.
The grass top 艹 covers the lower part like a canopy of lush greenery. Picture a garden where plants grow so thickly they form a roof of leaves.
For エン, imagine an endless green field where plants grow luxuriantly: endless -> エン, and the scene is one of thriving abundance.
Philadelphia fleabane (Erigeron philadelphicus); common fleabane