This is Smilax, also known as catbriar, greenbriar, and blaspheme vine (for the things people say when they encounter it.) The vine is very tough and woody, and many species have nasty thorns.

The young shoots and the tender tips of the growing vine are one of my favorite trail nibbles, tasting much like asparagus, with a hint of lemony tartness.

The root has a much more famous food history. The hard, woody root is the source of the flavoring used for sarsaparilla and real root beer.