I walked around my exercise trail through the TVA reservation Wednesday and there they were, same sprouts and leaves, fast growing as they had been mowed last year and were growing back from the stump, thousands of them. The leaves varied from plant to plant from the usual mulberry looking, heart shaped leaves, to exactly like Jim has in his pictures.
And I still don't know for sure what they are.
I drove by an abandoned, over grown building on my way to the trail, in front to the building the property was full of giant ragweed plants, definitely not the same plant as Jim has in his pictures but exactly the same plant as we used for spears in my youth.