Campanula Percisifolia (the plant with the violet and white flowers) is a beautiful plant with edible flowers, stalks and leaves. Ken Fern, of the invaluable website "Plants For A Future," lists it as one of his favorite perennial greens, and it makes an appearance on the PFAF list of Alternative Edible Leaves.
More importantly to us, it makes the PFAF list of plants for "Winter Salads." Personally, in summer I find the leaves both a little fibrous and spicy, and there are plenty of other greens--even perennial ones--that I'd rather eat. But in winter, it's always waiting, buried beneath the snow. In the cold, the leaves are softer, and sweeter and can even be eaten raw at times, though we usually cook them. They are high in vitamin C, making them helpful in the winter diet.
As a bonus, I think they have the best tasting flowers I've eaten. They have a definite sweet flavor and a nice texture.