Help with Weed Id, please

I'm in zone 6, PA. I'm trying to ID a vineing weed that is common along the edges of woods and fields and is in some of my garden beds. I'm fairly sure it's an annual. It's a thin vine with a very minimal root system that climbs into trees and shrubs and grows very vigorously once established. It has triangular alternate leaves, about 2 inches across, and unpleasant small prickles all along the vine that break off in your skin. It clings to shrubs with the prickles, and does not really twine around like bindweed. I haven't let any go to seed this year, but I seem to recall it gets small dark blue berries later in the season.
It's relatively easy to control by pulling (with gloves on!), I just want to put a name to it. I've tried several on-line weed id sites and didn't come up with it. Thanks for your consideration!
Cheers, Sue
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snipped-for-privacy@NOSPAMearthlink.net
Zone 6, South-central PA
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along the

fairly sure

that
established. It

unpleasant
clings to

bindweed. I

small
want to

didn't come

My guess is greenbrier. Although I now live in Missouri, I grew up in West Virginia (about 50 mi. from the PA border) and this greenbrier, which is a dead ringer for what you describe, was very common in fields and waste areas. I can't speak whether it is an annual or not, but the leaves, prickles and vining habit are characteristic.
Guy Bradley Chesterfield MO zone 6
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Polygonum perfoliatum

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