The form seems to fit but the leaves look darker and not as 'flimsy' on your plant and I'm not sure about the woody stem and speed of growth from seed.
Here is a picture of the bark now that we had a hard freeze. You can see where I scratched the bark on the part I cut and this is not knotweed. We have had a very hard freeze here but I marked the bark differrence from three years' growth to the two years' growth. In my first picture I posted you can also see the this years growth the stem is bright green not green with red throughout as in knotweed. Besides being a Master Gardener for 17 years I was graduated from Longwood Gardens plant series 1 & 2. Believe me when I tell you I know the difference between knotweed and a tree/shrub with bark. I don't know how else to show that this is a woody plant. Any further thoughts would help keep me sane.
Well Richard, it is definately something???????????? When I go down to take pictures next time I'll ask one of the interns who work at the arboretum, they seem to know everything. Until then I'll just keep guessing. I still think it many be A cercis chinensis cultivar of some kind. Let you know when I find out.
Can you get a close enough image of a leaf scar, or maybe at least count the bundle scars? May not help if it's an alien but native field guides do categorize on that basis.
I've been following this thread and now I see it marked as identified? What as please? 
Inquiring minds want to know; what was this identified as? 
