Phaseolus polystachios is a perennial twining vine, stem to 4 m long.
Leaves alternate, 3-parted, leaflets broadly egg-shaped, terminal leaflet 3- 8 cm long, lateral leaflets asymmetric, rough-hairy above, softly hairy below.
Flowers purple, pea-flower-shaped, about 1cm long, upper petal (standard) round, folded over the others, lower petal (keel) coiled, upper calyx lobes rounded, others broadly triangular, style coiled, hairy on upper side; inflorescence long-stalked, unbranched about 15 cm long; blooming July-Sept.
Fruit dry, hollow pod, flat 3-6 cm long, curved, splitting open to release seeds, the sides coiling, seeds 4-5, to 1 cm long, 0.6 cm wide, black to gray.
Wetland status: NL.
Frequency in NYC: Very infrequent.
Habitat: Moist to dry, open oak woods, thickets, edges, sandy soil.