Practical
Plants

Polygonum arenastrum

Small-Leaved Knotweed

an annual member of the Polygonum genus in the family Polygonaceae.

No photo available

Taxonomy and growth

Life cycle
annual
Height
0.3 m
Fertility
Self fertile, Insects, Self
Flower type
hermaphrodite
Pollinators
Insects, Self

Uses

Toxicity

Toxicity warning. The historical record reports a hazard for this plant. Do not use it to decide which parts are safe to eat or use medicinally.

This section contains historical Plants For A Future notes marked noncommercial.

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[21].

Edible uses

This section contains historical Plants For A Future notes marked noncommercial.

Young leaves and plants - raw or cooked[30][33]. Used as a potherb[35], they are very rich in zinc[34]. A nutritional analysis is available[36]. Seed - raw or cooked. Rather small and fiddly to utilize, they can be used in all the ways that buckwheat (Fagopyrum esculentum) is used, either whole or dried and ground into a powder for use in pancakes, biscuits and piñole[37][38][31][32][35]. The leaves are a tea substitute[35]. There are no edible uses listed for Polygonum arenastrum.

Medicinal uses

Historical medicinal uses. These records describe reported uses. They do not establish safety or effectiveness. Ask a qualified health professional before using any plant medicinally.

This section contains historical Plants For A Future notes marked noncommercial.

Knotweed is a safe and effective astringent and diuretic herb that is used mainly in the treatment of complaints such as dysentery and haemorrhoids. It is also taken in the treatment of pulmonary complaints because the silicic acid it contains strengthens connective tissue in the lungs[23]. The whole plant is anthelmintic, astringent, cardiotonic, cholagogue, diuretic, febrifuge, haemostatic, lithontripic and vulnerary[25][28][29][17][26][5][9][10][12]. It was formerly widely used as an astringent both internally and externally in the treatment of wounds, bleeding, piles and diarrhoea[25]. Its diuretic properties make it useful in removing stones[25]. An alcohol-based preparation has been used with success to treat varicose veins of recent origin[28]. The plant is harvested in the summer and early autumn and is dried for later use[29]. The leaves are anthelmintic, diuretic and emollient[18]. The whole plant is anthelmintic, antiphlogistic and diuretic[18]. The juice of the plant is weakly diuretic, expectorant and vasoconstrictor[18]. Applied externally, it is an excellent remedy to stay bleeding of the nose and to treat sores[25]. The seeds are emetic and purgative[25][22]. Recent research has shown that the plant is a useful medicine for bacterial dysentery. Of 108 people with this disease, 104 recovered within 5 days when treated internally with a paste of knotweed[23].

Material uses

This section contains historical Plants For A Future notes marked noncommercial.

Yields a blue dye that is not much inferior to indigo[4]. The part used is not specified, but it is likely to be the leaves. Yellow and green dyes are obtained from the whole plant[7]. The roots contain tannins, but the quantity was not given[19].

Environment

Range
Throughout Europe, including Britain.
Habitat
Waste places and roadsides, common throughout Britain[8].
Light
full sun
Shade tolerance
light shade
Water
moderate
Hardiness
Zone 5+
Soil textures
sandy, loamy, clay
Soil pH
very acid, acid, neutral, alkaline
Tolerances
high wind, maritime exposure
Wind
Yes
Maritime
Yes
Tolerates Nutritionally Poor Soil
No
Drought
intolerant

Propagation

This section contains historical Plants For A Future notes marked noncommercial.

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. Division in spring or autumn. Very easy, larger divisions can be planted out direct into their permanent positions. We have found that it is better to pot up the smaller divisions and grow them on in light shade in a cold frame until they are well established before planting them out in late spring or early summer.

Cultivation

This section contains historical Plants For A Future notes marked noncommercial.

Succeeds in an ordinary garden soil[1] but prefers a moisture retentive not too fertile soil in sun or part shade[16]. Repays generous treatment, in good soils the plant will cover an area up to a metre in diameter[1][25]. Prefers an acid soil[15]. Dislikes shade. Knotweed is a common and invasive weed of cultivated ground[28]. It is an important food plant for the caterpillars of many species of butterflies[24]. It also produces an abundance of seeds and these are a favourite food for many species of birds[25]. Plants seem to be immune to the predations of rabbits[20]. The flowers have little or no scent or honey and are rarely visited by pollinating insects. Self-fertilization is the usual method of reproduction, though cross-fertilization by insects does sometimes occur[25]. The plant also produces cleistogomous flowers - these never open and therefore are always self-fertilized[25]. The plant is very variable according to habitat and is seen by most botanists as part of an aggregate species of 4 very variable species, viz. - P. aviculare. L.; P. boreale. (Lange.)Small.; P. rurivacum. Jord. ex Box.; and P. arenastrum. Bor[8].

References

  1. F. Chittendon. RHS Dictionary of Plants plus Supplement. 1956 Oxford University Press 1951-00-00

    ↩1↩2

  2. Tanaka. T. Tanaka's Cyclopaedia of Edible Plants of the World. Keigaku Publishing 1976-00-00

  3. Coon. N. The Dictionary of Useful Plants. Rodale Press 1975-00-00 ISBN 0-87857-090-x

  4. Johnson. C. P. The Useful Plants of Great Britain.

    ↩

  5. ? A Barefoot Doctors Manual. Running Press ISBN 0-914294-92-X

    ↩

  6. Yanovsky. E. Food Plants of the N. American Indians. Publication no. 237. U.S. Depf of Agriculture.

  7. Grae. I. Nature's Colors - Dyes from Plants. MacMillan Publishing Co. New York. 1974-00-00 ISBN 0-02-544950-8

    ↩

  8. Clapham, Tootin and Warburg. Flora of the British Isles. Cambridge University Press 1962-00-00

    ↩1↩2

  9. Schofield. J. J. Discovering Wild Plants - Alaska, W. Canada and the Northwest.

    ↩

  10. Yeung. Him-Che. Handbook of Chinese Herbs and Formulas. Institute of Chinese Medicine, Los Angeles 1985-00-00

    ↩

  11. Kunkel. G. Plants for Human Consumption. Koeltz Scientific Books 1984-00-00 ISBN 3874292169

  12. Stuart. Rev. G. A. Chinese Materia Medica. Taipei. Southern Materials Centre

    ↩

  13. Reid. B. E. Famine Foods of the Chiu-Huang Pen-ts'ao. Taipei. Southern Materials Centre 1977-00-00

  14. Facciola. S. Cornucopia - A Source Book of Edible Plants. Kampong Publications 1990-00-00 ISBN 0-9628087-0-9

  15. Riotte. L. Companion Planting for Successful Gardening. Garden Way, Vermont, USA. 1978-00-00 ISBN 0-88266-064-0

    ↩

  16. Huxley. A. The New RHS Dictionary of Gardening. 1992. MacMillan Press 1992-00-00 ISBN 0-333-47494-5

    ↩

  17. Lust. J. The Herb Book. Bantam books 1983-00-00 ISBN 0-553-23827-2

    ↩

  18. Duke. J. A. and Ayensu. E. S. Medicinal Plants of China Reference Publications, Inc. 1985-00-00 ISBN 0-917256-20-4

    ↩1↩2↩3

  19. Rottsieper. E.H.W. Vegetable Tannins The Forestal Land, Timber and Railways Co. Ltd. 1946-00-00

    ↩

  20. Thomas. G. S. Perennial Garden Plants J. M. Dent & Sons, London. 1990-00-00 ISBN 0 460 86048 8

    ↩

  21. Bown. D. Encyclopaedia of Herbs and their Uses. Dorling Kindersley, London. 1995-00-00 ISBN 0-7513-020-31

    ↩

  22. Chopra. R. N., Nayar. S. L. and Chopra. I. C. Glossary of Indian Medicinal Plants (Including the Supplement). Council of Scientific and Industrial Research, New Delhi. 1986-00-00

    ↩

  23. Chevallier. A. The Encyclopedia of Medicinal Plants Dorling Kindersley. London 1996-00-00 ISBN 9-780751-303148

    ↩1↩2

  24. Carter D. Butterflies and Moths in Britain and Europe. Pan 1982-00-00 ISBN 0-330-26642-x

    ↩

  25. Grieve. A Modern Herbal. Penguin 1984-00-00 ISBN 0-14-046-440-9

    ↩1↩2↩3↩4↩5↩6↩7↩8↩9

  26. De. Bray. L. The Wild Garden.

    ↩

  27. Harris. B. C. Eat the Weeds. Pivot Health 1973-00-00

  28. Chiej. R. Encyclopaedia of Medicinal Plants. MacDonald 1984-00-00 ISBN 0-356-10541-5

    ↩1↩2↩3

  29. Launert. E. Edible and Medicinal Plants. Hamlyn 1981-00-00 ISBN 0-600-37216-2

    ↩1↩2

  30. Tanaka. T. Tanaka's Cyclopaedia of Edible Plants of the World. Keigaku Publishing (1976-00-00)

    ↩

  31. Coon. N. The Dictionary of Useful Plants. Rodale Press ISBN 0-87857-090-x (1975-00-00)

    ↩

  32. Yanovsky. E. Food Plants of the N. American Indians. Publication no. 237. U.S. Depf of Agriculture. ()

    ↩

  33. Kunkel. G. Plants for Human Consumption. Koeltz Scientific Books ISBN 3874292169 (1984-00-00)

    ↩

  34. Reid. B. E. Famine Foods of the Chiu-Huang Pen-ts'ao. Taipei. Southern Materials Centre (1977-00-00)

    ↩

  35. Facciola. S. Cornucopia - A Source Book of Edible Plants. Kampong Publications ISBN 0-9628087-0-9 (1990-00-00)

    ↩1↩2↩3

  36. Duke. J. A. and Ayensu. E. S. Medicinal Plants of China Reference Publications, Inc. ISBN 0-917256-20-4 (1985-00-00)

    ↩

  37. Grieve. A Modern Herbal. Penguin ISBN 0-14-046-440-9 (1984-00-00)

    ↩

  38. Harris. B. C. Eat the Weeds. Pivot Health (1973-00-00)

    ↩

Edit this page