Polygonum arifolium is an annual vining herb, 1-2 m, stem with hooked prickles, slender, reclining on other vegetation; ocreae membranous.
Leaves alternate, arrow-shaped, to 20 cm long, 15 cm wide, basal lobes triangular, divergent, hairs in tiny cushions below.
Flowers pink, white or green, radially symmetrical, 5-parted, fused at base, petals (tepals) 0.25 cm, rounded on back, styles 2; blooming and fruiting Aug.-Sept. (Hough 1983).
Fruit dry, one-seeded, achene, broadly lens-shaped, to 0.5 mm, shiny, brown. Seeds eaten by many birds and small mammals (Martin et al 1951).
Wetland status: OBL.
Frequency in NYC: Very infrequent.
Habitat: Open marshes, pond edges.