On the pond rocks? It is some kind of spreading sedum, that's great for hot, dry conditions like growing over rocks. Is spreads like wildfire, doesn't require much water, and has tiny yellow blooms in late spring/early summer.
Oh, if you meant the green flowers with tiny yellow blooms growing on the rock wall in the picture above the frog, that's Corydalis. It blooms in partly sunny spaces, especially along rock walls, and blooms from early spring through late fall. One of my favorite perennials!
