Sorbus?

I happened upon this plant tonight on the way back from the compost bin as the sun was about to go from behind the clouds to below the horizon. At first glance I thought it was another of the ubiquitous little Rosa multiflora that are popping up everywhere. But closer examination shows that it's more ash-like. My tree book shows that both the American and European Mountain Ashes (Sorbus americana & Sorbus aucuparia) look somewhat like this. These are those ornamental trees with the orange fruit clusters. The "real" ashes (those in the Fraxinus genus) seem to have finer teeth, and we've got a lot of little ash seedlings coming up that look subjectively unlike this.

Note the white spots on the ground. These are cherry blossom petals that fell off the big cherry tree in the middle of the woods this afternoon.

Update, May 26, 2011: This was apparently very tasty. A couple of days later, there was no sign of this plant, whatever it was.