There is definitely poison ivy that grows as a vine. I just whacked
some here in NJ yesterday that was growing up a tree in the woods at
the border of my lawn. The root was about 1 1/2" in diameter at the
base. It went a good 20+ feet up the tree. You're right about needing
the Roundup to be strong. I used it at about 10%, whiere 1 or 2% is
fine for most common broadleaf weeds and grass.