Willow Grass, Water knotweed, Longroot smartweed, Water smartweed

Polygonum amphibium

Physical Characteristics

Polygonum amphibium is a PERENNIAL growing to 0.3 m (1ft). See above for USDA hardiness. It is hardy to UK zone 5. It is in flower from July to September. The species is hermaphrodite (has both male and female organs) and is pollinated by Insects. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers wet soil and can grow in water.

Distribution

Most of Europe, including Britain, temperate Asia, N. America and S. Africa.

Habitats

Pond; Bog Garden;

Edible Uses

Edible Parts: Leaves Seed Shoots Edible Uses: Leaves - raw or cooked. The young shoots are eaten in the spring[257]. Seed - cooked[178]. It is rather small and fiddly to utilize.

Medicinal Uses

Astringent Depurative Pectoral Poultice Skin The whole plant, but especially the root, is astringent, depurative, skin[145, 172, 178, 207]. An infusion of the leaves and stems has been used to treat stomach pains and children with diarrhoea[257]. The root has been eaten raw, or an infusion of the dried, pounded roots used, in the treatment of chest colds[257]. A poultice of the fresh roots has been applied directly to the mouth to treat blisters[257].

Known Hazards

Although no specific mention has been made for this species, there have been reports that some members of this genus can cause photosensitivity in susceptible people. Many species also contain oxalic acid (the distinctive lemony flavour of sorrel) - whilst not toxic this substance can bind up other minerals making them unavailable to the body and leading to mineral deficiency. Having said that, a number of common foods such as sorrel and rhubarb contain oxalic acid and the leaves of most members of this genus are nutritious and beneficial to eat in moderate quantities. Cooking the leaves will reduce their content of oxalic acid. People with a tendency to rheumatism, arthritis, gout, kidney stones or hyperacidity should take especial caution if including this plant in their diet since it can aggravate their condition[238].