Polygonum lapathifolium is an annual herb to 2.5 m, variable, often very robust, rooting at lower nodes; nodes swollen, often reddish, sheaths without bristles, upper portion membranous, disintegrating with age leaving a pale green, short, more or less cup-shaped sheath with several heavy veins at base of leaf stalk.
Leaves alternate, lance-shaped, 5-25 cm long, to 6 cm wide, veins impressed above, surface often with dark splotch similar to P. persicaria and often with tiny, flat, shiny glands below or sometimes hairy below.
Flowers rose, white or pale green, 0.3- 0.4 cm long, petal lobes 4-5, most with 3 conspicuous veins hooked at tips in an upside-down anchor shaped pattern (use lens); Inflorescence branched, of slender, usually nodding spike-like racemes 1-10 cm long, 0.3-0.9 cm wide (Yatskievych 2006); blooming and fruiting July-Oct. (Hough 1983); often plants with flowers of different colors growing together.
Fruit dry 1-seeded (achenes), lens-shaped, brown to black, shiny.
Wetland status: FACW+.
Frequency in NYC: Occasional.
Habitat: Moist or wet soil with high to low nutrient content, open areas, gravel bars, mature plants somewhat shade tolerant (Sultan et al. 1998). Distinguished by nodding inflorescences (racemes) and anchor-shaped petal veins.