Curlytop Knotweed
Polygonum lapathifolium

Family: Polygonaceae

What it is like

Polygonum lapathifolium is a ANNUAL growing to 0.8 m (2ft 7in). See above for USDA hardiness. It is hardy to UK zone 5. 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 moist or wet soil.

Height (m): 0.8

Where it is found

Swampy thickets, shores, damp clearings and cultivated fields in N. America.

Temperate regions of the northern hemisphere, including Britain. S. Africa.

Conservation Status:

Countries/locations it is found in

How it is used

Food

Rating: 1

Young leaves - raw or cooked. Seed - raw or cooked. It is rather small and fiddly to utilize.

Seed: includes nuts, cereals, peas and beans.

Medicine

Rating: 1

The whole plant is antiseptic and astringent. An infusion has been used in the treatment of stomach complaints and fevers. The plant produces a soft white mass, a froth like that of soap. It is applied externally to burns.

Antiseptic: Preventing sepsis, decay or putrefaction, it destroys or arrests the growth of micro-organisms.

Astringent: Produces contraction in living tissue, reducing the flow of secretions and discharges of blood, mucus, diarrhoea etc.

Febrifuge: Reduces fevers.

Stomachic: Aids and improves the action of the stomach.

Other

Rating: 0

The plant produces a soft white mass, a froth like that of soap. It is used for bathing and washing clothes.

Soap: Plants used directly as a soap substitute.

How it is grown

Succeeds in an ordinary garden soil but prefers a moisture retentive not too fertile soil in sun or part shade. Repays generous treatment. Plants seem to be immune to the predations of rabbits.

Propagating it: Seed - sow spring in a cold frame. Germination is usually free and easy. When they are large enough to handle, prick the seedlings out into individual pots and plant them out in the summer if they have reached sufficient size. If not, overwinter them in a cold frame and plant them out the following spring after the last expected frosts.

Best place to grow: Bog Garden;

Habit: Annual

Hardiness: 4-8

Growth:

Soil: Light (sandy), medium, heavy (clay)

Shade: Semi-shade, no shade

Moisture: Moist, wet

Things to keep in mind

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.

Its other names

Local names

Synonyms

P. scabrum. Moench. Persicaria lapathifolium. (L.)S.F.Gray.