Stachys minima more commonly known as Dwarf Betony. Wikipedia states " The distribution of the genus covers Europe, Asia, Africa, Australasia and North America. Common names include heal-all, self-heal, woundwort, betony, lamb's ears, and hedgenettle. Wood betony, Stachys officinalis, was the most important medicinal herb to the Anglo-Saxons of early medieval Great Britain."
I first became aware of this plant when my friend Dave Meyer gave me one while visiting him, and when it bloomed, was I impressed. I've always thought highly of Stachys Hummelo and this is very similiar in habit only in about the third of it's size. The flower color is a little lighter in color but it stands up like Hummelo and covers the plant. I had it planted next to a Tradescantia 'Sweet Kate' in partial shade and the color combinations were striking. The deep flower color and light yellowish green leaves of the Tradescantia and the deep green leaves and lilacy purple color of the Stachys flowers were very complimentary. I have divided it several times at different times of the year and it just keeps on growing. I took these photo's at the Midwest Groundcovers trial garden several years ago.