Well, I'm going based on this, which is posted to the Forest Service: http://www.na.fs.fed.us/fhp/invasive_plants/weeds/queen-annes-lace.pdf It says it's "It is reported invasive in CT, GA, HI, KY, MD, MI, MO, NJ, OR, TN, VA, WA, WI, and WV." I live in southern MD right on the DC border so that made me nervous. It's a shame because it's a pretty plant and I have a front yard that slopes steeply down to the sidewalk that could use some covering.

I found the name: Pearcea hypocyrtiflora Here's a link with more pictures: http://www.gesneriads.ca/pearcea.htm This diminutive rhizomatous plant has very attractive and colorful foliage, as well as unusual brilliantly red flowers. The lobes of the flowers do not open except under optimum conditions. The flowers are probably hummingbird pollinated. They grow in colonies in tropical rain forests. Thanks, Joe Here is a link that might be useful: More info and pictures about this plant

It is sweet allysum, Lobularia maritima, This is an annual so generally not considered to be a groundcover. However it reseeds rather freely so once planted and left to flower, it will typically come back with such regularity that it almost appears to be a perennial groundcover.

Agree with Vernonia, common name is ironweed.