"King Henry" Viola
Violas are the easy-going, hardier, smaller, and more perennial cousins of pansies. Their gorgeous purple-blue edible flowers are held above the foliage in great numbers, and don't flop or get rain damage like larger flowers do. And they cover themselves with bloom over a long season, often wintering over in zones 3-8. Descended from the wild English Heartsease, (Johnny-jump-up in the states) they have all the charm of a wildflower, with the longer bloom, larger number of flowers, and more glowing color of a beloved cottage garden favorite. The flowers are not only edible, but actually taste pretty good, with a wintergreen overtone that complements salads, cold drinks, and cakes. They have herbal and skin-care uses as well.
Violas have an unusual seed strategy--the seed-bearing flowers are different from the purple flowers and are inconspicuous. Then when the seeds mature, the seedpods become dry and finally explode, scattering the seeds to quite a distance, a process known as "ballistic seed dispersal."