"Marie Louise", named for Marie Louisa, the second wife of Napoleon Bonaparte, who was a great admirer of scented violets.  It is considered the hardiest of the Parmas, although I cannot attest to this.  It is similar to "Duchesse de Parme" but the lavender is much deeper.   Parma violets are the most fragrant of the scented violets. While they are perennial, they are tender and not winter hardy in most parts of the US so should be potted and wintered indoors. It is written that they will survive 20 degrees Fahrenheit, but not for long, and in my own experience, not at all. I suggest Zones 7 (with protection) to 10.  To make the plants stronger and to produce more blooms, cut off the runners in late summer/early fall. They will perfume an entire room, so the effort is worth it. (1865 but believed to be earlier)