- Name also: Pale Smartweed, Curlytop Knotweed, Willow Weed
- Lat. synonym: Polygonum lapathifolium
- Family: Dock Family – Polygonaceae
- Growing form: Annual herb.
- Height: 20–80 cm (8–30 in.). Stem erect, swollen above nodes.
- Flower: Regular, approx. 1,5 mm (0.06 in.) long (elongates in fruit). Perianth consists of usu. 5 yellowish or pink segments, united from base to halfway. Pedicel and perianth with yellow glands. Pistil formed from two fused carpels. Basally slightly united styles 2. Stamens 6. Inflorecence a dence spike.
- Leaves: Alternate. Stalked, hairless or densely hairy beneath. Blade 5–20 cm (2–8 in.), lanceolate to narrow-elliptic, pointed or blunt, often with a dark blotch in the middle. Stipules fused into a stem-enclosing sheath (an ochrea) that is loose and hairless or very short-hairy at the mouth.
- Fruit: Brown, roundish but flat achene, approx. as long as the perianth.
- Habitat: Shores, arable land, waste ground, gardens, rubbish tips, and roadsides.
- Flowering time: July–September.
Pale persicaria is a variable annual often associated with old habitation. It is not very demanding but prefers nitrogen-rich soil. On fields this species is a troublesome weed. Its seeds remain viable for decades and may pass the alimentary canal of cattle intact.
Pale persicaria is divided in two subspecies, which are the more common ssp. pallida and more reddish ssp. lapathifolia. Fairly rare redshank (P. maculosa) looks quite like pale persicaria. It differs in that it lacks glandular dots and usu. has a long-hairy ochrea, and by the styles that are fused from the base to halfway.