Persicaria nepalensis aka Nepalese Smartweed

Persicaria nepalensis is also known as Nepalese smartweed. It belongs to Polygonaceae, the knotweed family. Its older name is Polygonum nepalense. Its home range spans eastern and southern Africa, including Madagascar. It also spans tropical and subtropical Asia, reaching Russia’s Far East. It is not native to Britain or Ireland. It now grows beyond its home range. This spread includes the Americas and the Pacific.

This slim plant lives for one year, making it an annual. It grows about 1 foot (0.3 m) tall. Some accounts give a top height near 1.6 feet (0.5 m). Its stems spread out or lie on the ground. They often root where leaf nodes touch the soil. These nodes are the points where leaves join stems. This helps it spread across the ground near it. It blooms from June through September. Insects carry pollen between the flowers. Each flower has both male and female organs. Seeds ripen from July through October. The plants form many seeds.

In the wild, it grows in damp, shaded spots. These include mountain woods in Japan and damp sites around Srinagar. It also grows on open, rocky slopes in Nepal. Sources say moist or wet soil suits it in gardens. It grows in sand, loam, or clay. The soil can be mildly acid, neutral, or mildly alkaline. It grows in sun or light shade. The tropical plant source favours fairly sunny sites in temperate climates. Soil should hold moisture but not be too rich. How well it copes with cold in Britain remains unclear. PFAF suggests growing it there as an annual, sown in spring.

Suggested sites include damp woodland edges and bog gardens. Its spread can also make it a weed. The sources differ on this risk. PFAF lists no weed potential. Useful Tropical Plants reports that it infests crops. It causes problems in tea plantations and other highland tropical crops. It can persist in Britain with no reported weed problems. Its shallow roots make it easy to pull or hoe. These accounts list no pests or diseases specific to this species.

People gather it for food and other local uses. They eat young leaves and shoots raw or cooked. The seeds are edible, but their small size hinders use. Folk remedies use root juice for fever. They also use root paste on wounds. These uses do not prove that the treatments work. People squeeze the plant for use in washing clothes. The supplied sources establish no toxicity finding specific to this species.