Polygonum hydropiper  (Persicaria hydropiper) marsh pepper knotweed Polygonaceae POHY*; Bx, pb; Q; R;

Polygonum hydropiper.erbe.altervista.org (2)

Polygonum hydropiper.erbe.altervista.org (Accessed 6/2015).

Polygonum hydropiper is an annual herb to 60 cm tall, roots fibrous, stems erect to sprawling, branching freely at base, plant peppery tasting, stems often reddish; leaf sheaths rough, margins with bristles to 0.6 cm long, turning brown and disintegrating with age, nodes swollen, concealing small self fertile flowers. 

Leaves alternate, narrow, to 16 cm long, 2 cm wide 

Flowers greenish-white to pink, radially symmetrical; petals 5 sprinkled with tiny yellowish glandular dots; inflorescence linear, spike-like (racemes); blooming and fruiting July-Oct. (Hough 1983). 

Fruit dry, achenes, dark brown usually 3-angled, sometimes lens-shaped, surface dull. Similar to P. punctatum. Seeds eaten by birds (Martin et al. 1951). 

Wetland status: OBL. 

Frequency in NYC: Very infrequent. 

Origin: Eurasia. 

Habitat: Wet, open areas, high nutrient, organic soil, pH 6.0, seedlings tolerant of flooding (Sultan et al. 1998). 

Notes: Sap acrid, may cause photosensitization (Kingsbury 1964).