Maybe Moss Rose? But it sure looks like this double flowered chamomile. Are the leaves succulent? Does it have a scent? Here is a link that might be useful: double flowers

Okay, as a follow-up piece of information, I just discovered that the more bare part of the hill has a few jack-in-the-pulpits in the shadier parts, fi that gives any context as to soil and light conditions (though from what I've read, these wildflowers can grow in a variety of conditions).

I'm not sure why the extreme feelings about pachysandra - it is no more aggressive or potentially invasive than vinca :-) And just as easy to control the spread if attempting to encroach on areas where not wanted. It is extremely cold tolerant, evergreen and prefers a shady position, much the same as vinca and they can be used interchangeably. The harsher the zone and the growing conditions, the less likely either of these will get out of control. It is important to remember that one of the primary functions of a groundcover is to cover real estate, so a more or less aggressively spreading habit is desirable. With any kind of groundcover, some sort of routine maintenance is going to be necessary to keep the plants restricted to their specific area - nothing is plant and forget :-) Otherwise, taller growing but more clumping forming shrubs or perennials may be appropriate.

I have PLENTY of both regular and variegated kerria japonica if you want some suckers, also clerodendrum trichotoma (harlequin glorybower -- a nice five-foot shrub that blooms in white fragrant flat panicles, then the berries turn blue while the brachts stay maroon, and then later the leaves go golden before they drop -- definitely a three-season shrub, though again it DOES sucker). I also have a large abelia (really a part-sun shrub, but truly blooms all summer) that I would like to dig up and replace with a blueberry. I live in Lanham, near NASA -- is that close enough for you? LynnT