Polygonum erectum erect knotweed Polygonaceae K, p (Z. Wang);

Polygonum erectum.Zihao Wang.Prospect Park, Brooklyn, NY.

Polygonum erectum.Zihao Wang.Prospect Park, Brooklyn, NY. 2015.

Polygonum erectum is an annual to 50 cm tall, branched; a membranous leaf sheath (ocreae), 0.4-1 cm long, surrounds the plant stem just above the leaf stalk (petiole).Stems erect, to prostrate and upturned at ends of branches.

Leaves green to bright yellow-green, small, of differing sizes, (heterophyllous) the larger, stem leaves,  3-6 cm wide, 1-3 cm long, those just below inflorescences are smaller than ordinary stem leaves; petiole jointed at base, at juncture with the leaf sheath.

Flowers very small, white to yellow-green, 5 parted, petals and sepals the same (tepals), fused at base and becoming larger in fruit; inflorescence of small clusters in leaf axils.

Fruit dry, 1-seeded achene, 3-sided, brown, striped and finely warty (papillose). Use lens.

Wetland status: FACU

Frequency in NYC: Very infrequent.

Origin: Native.

Habitat: Open soil of disturbed sites, shores.