Beautiful purple flowers in April, 2 feet tall. Often mistaken for phlox, but blooming 2 months earlier, a fantastic contrast companion to late-blooming daffodils, Kerria, & Viburnum.
Technically a biennial that reseeds so readily that it acts like a perennial, so long as you don't accidentally remove seedlings, which are easily pulled if need be. Full sun to full shade -- yes, you read that right!