noun
sweet violet (Viola odorata)
Refers specifically to the flowering plant Viola odorata, known for its fragrance.
庭にニオイスミレが咲いている。
Sweet violets are blooming in the garden.
Compound of 匂い (nioi, 'scent') and 菫 (sumire, 'violet'). The exact historical derivation is uncertain, but the name straightforwardly describes the fragrant violet.