Herbs & Plants

Japanese knotweed

Botanical Name :Fallopia japonica

Family: Polygonaceae
Genus: Fallopia
Species: F. japonica
Kingdom: Plantae
Order: Caryophyllales
Synonyms. :Polygonum cuspidatum, Reynoutria japonica,Polygonum sieboldii – De Vriese
Common Names:Polygonum cuspidatum, Polygonum sieboldii, Reynoutria japonica, Fallopia japonica, Polygonum cuspidatum, Reynoutria japonica, Fleeceflower, Himalayan fleece vine, monkeyweed, Huzhang, Hancock’s curse, elephant ears, pea shooters, donkey rhubarb, sally rhubarb, Japanese bamboo, American bamboo, Mexican bamboo,

English names for Japanese knotweed Fleeceflower, Himalayan fleece vine, Monkeyweed, Huzhang (Chinese:  pinyin: Huzhàng), Hancock’s curse, elephant ears, pea shooters, donkey rhubarb (although it is not a rhubarb), sally rhubarb, Japanese bamboo, American bamboo, and Mexican bamboo (though it is not a bamboo). There are also regional names, and it is sometimes confused with sorrel.

Habitat :Native to eastern Asia in Japan, China and Korea. In North America and Europe the species is very successful and has been classified as an invasive species in several countries.

It can be found in 39 of the 50 United States and in six provinces in Canada. It is listed as an invasive weed in Ohio, Vermont, Virginia, New York, Alaska, Pennsylvania, Oregon and Washington state.[6] The species is also common in Europe. In the UK it was made illegal to spread Japanese knotweed by the Wildlife and Countryside Act 1981. It is also classed as “controlled waste” in Britain under part 2 of the Environmental Protection Act 1990. This requires disposal at licensed landfill sites

Japanese knotweed is a large, herbaceous perennial plant, has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not closely related. While stems may reach a maximum height of 3–4 m each growing season, it is typical to see much smaller plants in places where they sprout through cracks in the pavement or are repeatedly cut down. The leaves are broad oval with a truncated base, 7–14 cm long and 5–12 cm broad, with an entire margin. The flowers are small, cream or white, produced in erect racemes 6–15 cm long in late summer and early autumn.


Japanese knotweed was introduced from Japan in 1825 as an ornamental plant. Although attractive, it has become a notoriously invasive plant. However it also has edible and medicinal properties and contains resveratrol a remarkable substance with anti ageing properties. It is also noted for attracting wildlife.

Closely related species include giant knotweed (Fallopia sachalinensis, syn. Polygonum sachalinense) and Russian vine (Fallopia baldschuanica, syn. Polygonum aubertii, Polygonum baldschuanicum).

Now in the U.S. and Europe, Japanese knotweed is widely considered an invasive species or weed. It is listed by the World Conservation Union as one of the world’s 100 worst invasive species.

The invasive root system and strong growth can damage foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites. It can also reduce the capacity of channels in flood defences to carry water.

It is a frequent colonizer of temperate riparian ecosystems, roadsides and waste places. It forms thick, dense colonies that completely crowd out any other herbaceous species and is now considered one of the worst invasive exotics in parts of the eastern United States. The success of the species has been partially attributed to its tolerance of a very wide range of soil types, pH and salinity. Its rhizomes can survive temperatures of ?35 °C (?31 °F) and can extend 7 metres (23 ft) horizontally and 3 metres (9.8 ft) deep, making removal by excavation extremely difficult. The plant is also resilient to cutting, vigorously re-sprouting from the roots. The most effective method of control is by herbicide application close to the flowering stage in late summer or autumn. In some cases it is possible to eradicate Japanese knotweed in one growing season using only herbicides. Trials in the Queen Charlotte Islands (Haida Gwaii) of British Columbia using sea water sprayed on the foliage have demonstrated promising results, which may prove to be a viable option for eradication where concerns over herbicide application are too great.

Two biological pest control agents that show promise in the control of the plant are the psyllid Aphalara itadori and a leaf spot fungus from genus Mycosphaerella.

Cultivation :
A very easily grown plant, it succeeds in ordinary garden soil in sun or shade, though it prefers a moist soil in partial shade. Japanese knotweed is an extremely invasive plant capable of sending up new shoots at a considerable distance from the main clump and also of growing up through tarmac. The sub-species cuspidatum is the form that is most likely to cause problems. It is considered to be a pest in many areas, where it is forming large clumps in the wild and out-competing native species. If grown in the garden it should be planted within a strong barrier to contain its roots. The sub-species compacta is only about 70cm tall and is far less invasive, but should still not be grown in small gardens. A report on the Natural History Programme stated that Japanese knotweed is actually becoming a very valuable habitat for spiders, frogs, grass snakes and many other creatures. Its hollow stems allow a wide variety of insects and other small creatures to overwinter and find hiding places, thus a greater abundance of food is provided for insectivores such as frogs, who are themselves eaten by grass snakes. In areas of north Wales where Japanese knotweed has run rife, it is now the primary habitat for grass snakes. Plants seem to be immune to the predations of rabbits. Often cultivated as a dye and a medicinal plant. Very closely related to P. conspicuum. Dioecious, male and female plants must be grown if seed is required.

Seed – sow spring in a cold frame. 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.

Edible Uses:
Edible Parts: Leaves; Root; Seed; Stem.

The young stems are edible as a spring vegetable, with a flavor similar to mild rhubarb. In some locations, semi-cultivating Japanese knotweed for food has been used as a means of controlling knotweed populations that invade sensitive wetland areas and drive out the native vegetation. Some caution should be exercised when consuming this plant because it contains oxalic acid, which may aggravate conditions such as rheumatism, arthritis, gout, kidney stones or hyperacidity.

Young shoots in spring – cooked. They can be used as an asparagus substitute. They have an acid flavour and can also be used as a rhubarb substitute in pies, fruit soups, jams etc. Older stems and shoot tips – cooked. They taste like a mild version of rhubarb. Seed – raw or cooked. It is rather small and fiddly to utilize. The seed can also be ground into a powder and used as a flavouring and thickener in soups etc, or can be mixed with cereals when making bread, cakes etc. The root is sometimes eaten.

Medicinal Uses:

Antiphlogistic; Antitumor; Depurative; Diuretic; Emollient; Febrifuge; Stomachic; Vulnerary; Women’s complaints.
Both Japanese knotweed and giant knotweed are important concentrated sources of resveratrol, replacing grape byproducts. Many large supplement sources of resveratrol now use Japanese knotweed and use its scientific name in the supplement labels. The plant is useful because of its year-round growth and robustness in different climates.

Japanese knotweed is a concentrated source of emodin, used as a nutritional supplement to regulate bowel motility. The roots of Japanese knotweed are used in traditional Chinese and Japanese herbal medicines as a natural laxative. The active principle responsible for the laxative effect is emodin, present in its natural form as a complex of its analogs. Emodin has a mild laxative effect in doses of 20 to 50 mg per day.

Hu Zhang root extract is a traditional Chinese medicinal treatment.In China, the root was used medicinally to treat menstrual and postpartum difficulties.

Methanol extracts of the roots of Polygonum cuspidatum (Polygonaceae), traditionally used in Korea to maintain oral health, were shown to reduce the viability of Streptococcus mutans and Streptococcus sobrinus as well as inhibit sucrose-dependent adherence, water-insoluble glucan formation, glycolytic acid production and acid tolerance. The authors suggested that inhibitory effects may be mediated by the presence of alkaloids, phenolics and sterol/terpenes in the extract.

You may click to see :Medicinal Uses for Japanese Knotweed :

Other Uses:
Japanese knotweed flowers are valued by some beekeepers as an important source of nectar for honeybees, at a time of year when little else is flowering. Japanese knotweed yields a monofloral honey, usually called bamboo honey by northeastern U.S. beekeepers, like a mild-flavored version of buckwheat honey (a related plant also in the Polygonaceae).

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.

The information presented herein is intended for educational purposes only. Individual results may vary, and before using any supplements, it is always advisable to consult with your own health care provider


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