Moneywort (Lysimachia nummularia) 2008-7-10 Finger Lakes, NY

-introduced, can become invasive under the right conditions (moist soil)
-in the same genus with Loosestrifes
-roundish, opposite leaves on stems that grow up to 3'
-the 3' delimitation on growth doesn't matter much, it seems to me, because it is said to root freely at the nodes, its main means of propagation
http://www.friendsofthewildflowergarden.org/pages/plants/moneywort.html
- given only a casual glance it might be confused with Lesser Celandine, or Marsh Marigold, all lower to the ground and lots of green and yellow