@Groundskeeper: It's not hewitt's Double - the flowers are tiny fluffs growing from a long sprig, and the leaves and tiny ferms close to the ground. 

@Groundskeeper: Thanks for the tips.... I think I found it! Thalictrum polygamum seems to be the closest to what I found. It's growing wild under a willow tree in some poor damp clay. I would hate to lose it - and would LOVE to have more. Any ideas?

@Claire: But then again, mine is not tall - it's probably just a foot high.... hmmm.... maybe it's not Thalictrum polygamum after all.

@Claire: I hope a sure id comes in from another YGS member, but meanwhile, yours sounds likely. If it's already happy on your damp clay why would it go away? To have more, let it make seeds and learn to know the seedlings and transplant them. Or start the seeds yourself. Maybe you have a unique plant and your seedlings will be wonderful? Something like that happened in my garden with a peony seedling. It turned into a peony like no other. It might even be interesting to peony growers. We'll see.

@Claire: maybe the clay and the shade cut its height?

@BotanicalBrain: Yes! I think you are right! I have marked the spot where it grows, now that the flowers are gone, so I can make sure I don't accidentally dig it out. Any tips on propagation? I'd love to have more.

@Claire: Great! If your clump is large enough, divide it in early spring. It's also easily grown from seed, though plantlets may not be true to parent. Still, the wild-type meadowsweet is pretty in its own right.