Canadian Gardening: the mysterious green compositae, 0 by hortensia

hortensia wrote:
anyone know what this strange thing is? Appeared in my garden last year, and seeded all over the place. I THINK it is an annual. Seedling heights vary from 2-5 feet; the stems are green, or, on the best forms IMO maroon. very airy and graceful, doesn't need staking. A lot like a coreopsis with attitude; but the flowers are GREEN. mint leaf green.

I have had a hard time taking a good picture of it. but here are the first -- the whole plant