A cold-hardy tree with no bark? This plant confuses me.

[biwa]

Can a cold hardy (zone 7) tree exist that has no bark? I found a tree growing in Virginia that looks like the "elephant ear" plants I see in nurseries. If it has bark, the bark is completely green. I cut a young branch in half and it had a pale green center about 5 mm in diameter, surrounded by a 2 mm thick "bark" made of darker green flesh.

I watched the plant grow and it gets bigger and bigger every year, just like a tree, even though it looks like a weed to me. When it was about as tall as a 2-story house, it started making nuts in bunches (like the way grapes grow).

Can someone explain this plant to me? I have a few questions about it:
1. How can it survive the winter without any bark?
2. Because the branches are green, does this mean that they can photosynthesize by themselves, even if I cut the leaves off?
3. Where are the capillaries that carry water to the top of the plant? Are they in the darker green "bark" area of the branches or are they in the paler green centers? Or in both?