Polygonum coccineum

Muhl. ex Willd.

Water smartweed

Polygonaceae Edible: Leaves, Seeds Potential hazards — see below

iNaturalist· cc-by

iNaturalist· cc-by-nc

Summary

A perennial herb reaching 0.5 m tall, hardy to UK zone 5. Hermaphroditic flowers are insect-pollinated. Grows in light sandy, medium loamy, or heavy clay soils across a range of pH levels from mildly acidic to mildly alkaline. Tolerates semi-shade or full sun and thrives in wet conditions, even growing in water.

Description

Edible Uses

Young shoots are collected in spring and used cooked. Seeds can be eaten raw or cooked, though they are small and fiddly to work with.

Medicinal Uses

None known

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.

Distribution

It is a temperate plant.

Where It Grows

North America, USA,

Cultivation

A water plant, succeeding in shallow water or a bog garden. Tolerates most soils but repays generous treatment. The stems of this plant root at the nodes wherever they come into contact with the soil. Plants seem to be immune to the predations of rabbits.

Propagation

Sow seed in spring in a cold frame; germination is generally free and easy. Once seedlings are large enough to handle, prick them out into individual pots and plant out during summer if they have reached sufficient size, or overwinter in a cold frame and plant out the following spring after the last expected frosts. Division can be done in spring or autumn and is very straightforward — larger divisions can go directly into permanent positions, while smaller ones do better potted up and grown on in light shade in a cold frame until well established before planting out in late spring or early summer.