Persicaria perfoliata

Persicaria perfoliata is a species of flowering plant in Polygonaceae.
It is a trailing herbaceous annual vine with barbed stems and triangular leaves.
Distinctive circular, cup-shaped leafy structures, called ocreas, surround the stem at intervals. Flower buds, and later flowers and fruits, emerge from within the ocreas. Flowers are small, white and generally inconspicuous. The fruits are metallic blue, each segment containing a single glossy, black or reddish-black seed