I forgot all about this plant, since it has long ceased blooming and obedient plant, butterflyweed and blue lobelia have crowded the border and are demanding attention from the eye and the brain. The picture is from early July. The plant is about a foot high. The flowers, of which there are a few, sit atop a single stem. I initially identified this wrong, but thanks to an attentive blog reader I now know what I am dealing with. I am not sure where it came from but it may have hitchhiked a ride with some of the other plants I acquired, either as a seed or a small seedling. Anyway, it seems to like the location which is a bit sunnier (6 hours +) than the rest of the woodland garden.
this appears to be Spigela marylandica (Indian Pink)