Mile-A-Minute
Persicaria perfoliata (CISMA, GoBotany, Wikipedia, USDA - NISIC) is a herbaceous annual vine with barbed stems and triangular leaves.
It is aggressively invasive. While we haven't had any confirmed sightings in Acton, it has been seen in Massachusetts.
Removal
Mechanical removal by pulling up the plant worked at an infestation in Westford.
Any removed plant material should be bagged, labelled, and disposed of by the Acton Natural Resources Dept.
Common Mis-Identifications
Hedge False Bindweed (Calystegia sepium, Wikipedia) also has a triangular leaf, but has a V-shaped notch where the stem attaches to the leaf (versus the fully triangular Mile-a-minute leaf).
Short-stalked False Bindweed (Calystegia silvatica, Wikipedia) also has a triangular leaf, but has a square-shaped notch where the stem attaches to the leaf.