Oops, planted it and lost the tag. It's growing quite happily in zone 5A (USDA zone 4) in light shade and clay soil.
1 Answer
It looks like Chrysogonum virginianum. Here is an excerpt from a nursery site:
Commonly known as Goldenstar or Green and Gold, Chrysogonum virginianum is a beautiful wildflower that is native to the eastern United States. It is one of the finest flowering ground covers for the sun or shade garden, bearing bright yellow star-shaped flowers that will lighten up even a patch of deep shade.