That may be crossvine, which I too have mistaken for snakeroot.

Snakeroot leaves alternate.

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Samantha is right, Mary, your vine is undoubtedly crossvine - I've made the same mistake myself, because the leaves do look very similar. I've got lots of Va. snakeroot, and it's never gotten more than about 2' tall - if yours is growing up a tree, that alone eliminates the possibility of it being Va. snakeroot. It's still a wonderful host plant for pipevine swallowtails, because they can eat a plant down to the ground, and it'll regrow in no time!
Here's a picture of one of mine - the leaves are alternate in a sort of irregular fashion -
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And here's a picture of some of my crossvine - the leaves, as Sam says, are opposite, and they're longer and thinner than Va. snakeroot leaves -
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Sherry

So I should leave it? You say it is still a host plant for the Pipevines? Then I wonder why the cats didn't take to it? I put a tender end of the vine in a florist tube and put a newly hatched cat on it and he kept crawling off of it. It has grown pretty quickly this spring and I know everyone says the Snakeroot doesn't. I was weeding in the area today and found another piece in the spot of the original - and it looks the same. The other piece that I took pictures from is about 2 ft away. I wonder if I could have been sent this instead of the Snakeroot. I have never seen Crossvine in my yard before and I sure didn't buy it.

No, I meant that Va. snakeroot is a host plant for pipevine swallowtails, not crossvine. Crossvine is reportedly a host for certain types of sphinx moths, can't remember which ones, and the flowers in the spring are beautiful. Plus it's a good hummingbird plant, and it's very easy to grow.
Sherry

Thanks for clarifying, Miss Sherry. There goes my hopes of having something for the Pipevines. I have the white veined Pipevine but they don't seem to do well on it either. I have lost all that I tried to raise this year.

BTW, only one of my Giant Swallowtails made its chrysalis out of the two cats I raised. Both got so much bigger than any of my other Giant Swallowtails that I raised in the past. The 2nd of the two this year started making its chrysalis and I accidently moved the container not realizing it was in the process. It seemed to stop and never went back to finishing the chrysalis. I felt so bad as it was a beauty of a cat.