Persicaria longiseta aka Bristly Lady's Thumb

Persicaria longiseta is an annual in the knotweed family, Polygonaceae. Its common name is Oriental lady's thumb. The RHS lists Polygonum longisetum as a synonym. Its native range spans much of Asia. Kew places it from Pakistan to the Russian Far East and Philippines. Records also include China, Korea, Japan, Taiwan, and parts of Southeast Asia. It is not native to Britain or Ireland.

The plant grows to about 1.6 feet [0.5 metres] tall. As an annual, it completes its life cycle within one year. Plants For A Future records flowers from May to June. Its seeds ripen from June through August. Each flower has both male and female organs. The supplied species account gives no detail on flower colour. It also gives no leaf, stem, or fruit description. The RHS describes these features only for the wider genus.

Wild habitats point to a plant of damp ground. In Japan, it grows in wet, sunny grassland at low elevations. Chinese records include moist valleys, stream banks, ditches, and watersides. Some of these sites lie in shade. In China, its range reaches about 10,170 feet [3,100 metres] above sea level. Plants For A Future lists it for bog gardens. The species account says it prefers moist or wet soil. It accepts sandy, loamy, and clay soils across mildly acid to mildly alkaline conditions. It can grow in sun or light shade.

Its cold tolerance in Britain remains uncertain in the supplied account. No firm hardiness zone is given. Plants For A Future describes spring sowing in a cold frame. It reports that seeds germinate with little trouble. Seedlings can move into separate pots once large enough to handle. The account suggests summer planting when plants have reached enough size. Its broader cultivation notes draw on the genus, not species trials. Those notes do not establish this plant's pest or disease resistance.

Young leaves can be eaten raw or cooked. The account treats them as an emergency food rather than a staple. Seeds can also be eaten raw or cooked. Their small size makes them awkward to prepare. Plants For A Future gives edibility a low score. It records no known medicinal or other uses. Its safety warnings concern related plants, not confirmed findings for this species. The supplied evidence therefore does not establish a species-specific toxicity rating.