Kim,

On the more mature parts of the vine, are there thorns?

Nope, no thorns. I'm reasonably sure it's perennial (the area it's growing in had been mowed several times, and when the mowing stopped it sprang up in full glory), and it grows in full sun, but that's all I know about it.

Some species of discorea.(Dioscorea? I find both spellings.) Try doing a Google image search and comparing pics to decide which species you have. Here in my zone, they're ALL horribly invasive!