I agree with fatamorgana: I don't want to cut it down if that's not what it is. I took a few more pics to see if it helps. Fata, you are right about it being more than one plant. There are three. Here is a pic of the three "trunks." Here is a picture of some new growth on the medium-sized one. Here is one "frond/branch" in almost its entirety. And this picture shows where the "fronds/branches" attach to the main stem or trunk.

in my garden.. native or not.. its an invasive weed .. kill them by the bazillions.. do NOT let them seed see link ken Here is a link that might be useful: link

It is NOT a horrible weed. It's a native vine, perfectly hardy, useful and of value to the creatures that live in the area that it is native to. It has beautiful fall color, berries that birds love. It does have tiny holdfasts to climb with, so be mindful of where you let it climb. It is the host plant for Sphinx moths and others.

Spurge. Ants love them! Use a notched weeder and slice through the central stem and you can remove the whole plant in one piece.