Japanese Knotweed

Japanese Knotweed
Japanese Knotweed (Fallopia japonica) is a species of herbaceous perennial plant of the Polygonaceae family native to eastern Asia, naturalized in Europe in a wide variety of wetlands.

This herb is very strong from China, Korea, Japan and Siberia. It is grown in Asia where it is known for its medicinal properties. Naturalized in Europe and America, it has become a major invasive species and is also included in the list of the International Union for Conservation of Nature of the 100 species of greatest concern.


* Reynoutria japonica Houtt. = Fallopia japonica var. japonica

Some authors accept the name of Reynoutria japonica

* Polygonum cuspidatum Sieb. & Zucc.

This is the term generally used by biologists and chemists (especially if they are Asian)

o Polygonum cuspidatum var. compactum (Hook f.) Bailey = Fallopia japonica var. compacta
* Polygonum zuccarinii Small
* Pleuropterus cuspidatus (Sieb. & Zucc.) Moldenke
* Pleuropterus zuccarinii (Small) Small

Philipp Franz von Siebold, medical officer of the East India Company stationed in Nagasaki between 1823 and 1829, harvest some of this wild feet. It will introduce in his garden of acclimatization in 1825, in Leiden as an ornamental, and forage melliferous. She has appeared in France the first time in 1939.

This large vigorous plant has hollow stems erect, reddish, similar to bamboo canes, 1 to 3 m high. Its growth may be several centimeters per day (from 1 to 8 cm after Brock). Aerial stems die in winter and only persistent buds at ground level (this is a hemicryptophyte).

The lower leaves broadly ovate-triangular reach 15-20 cm long and are abruptly truncated at the base. They are alternate.

Small white flowers appear in September-October are arranged in panicles in the axils of leaves (at the ocher). They include persistent tepal 5, 8 stamens and 3 styles. The fruit is a achenes 2-4 mm long. Pollinated by insects, the flowers provide a source of nectar at a time of year when flowers are very rare. In France, the seeds are of low fertility and reproduction is mainly by vegetative propagation through long rhizomes, fragments of dispersed rhizomes or stem cuttings.

The plant is considered by Beerling et al as gynodioique: it includes individuals male-sterile and hermaphrodite individuals. No male-fertile individual is known in Britain for the var. japonica.

For Lambinon and collaborators, the flowers of the wild (in Belgium and northern France) "in hermaphroditic appearance at a young age, behave as unisexual - and dioecious individuals-the so-called female flowers (or more "male-sterile") show small anthers included in the remaining Perigon and stigma well developed, while the so-called male flowers (or better-fertile males ") have their anthers and exsertes producing pollen. Each colony, spreading by vegetative propagation, is normally made up of individuals like them. "

Japanese Knotweed likes alluvial areas and the banks of rivers where moisture and nutrient rich substrate allows for optimal growth, leading to monospecific stands. It can form large dense thickets. It is also found in the milieux ruderalises (roadsides, around gardens, abandoned lots). It is better suited to acidic than alkaline land.

It is widespread in Western and Central Europe. It has colonized the whole of France.

It can be destroyed in a year or two thanks to the planting nettles the nettles kill knotweed.


* Reproductive organs:
o Type of inflorescence: spike of Cymes triflora
o distribution of the sexes: hermaphrodite
o Type of pollination: anemogame
o Flowering Period: Late July to September
* Seed:
o Type of fruit: achenes
o Mode of spread: barochore

Most seeds from hybrid individuals are not viable and the major mode of spread of Japanese knotweed is growing.

* Habitat and Range:
o Habitat type: Brownfields and perennial borders medioeuropeannes, eutrophiles, mesohydriques to mesohygrophiles
o Range: introduced (East Asia).


* In Europe, it is a nectar plant for beekeepers interesting because it blooms in late summer, when few flowers remain. But for this, the Japanese knotweed have been dispararaitre other flowering plants, indigenous them. Beekeepers from the north-eastern United States make it a honey monofloral called "honey bamboo (bamboo honey), dark brown, full-bodied like buckwheat honey.

* Use food and medicine in Japan

The young shoots are eaten raw or cooked. In spring, young shoots, similar to bamboo, are harvested before the stems and leaves separate. Removing the bark and eat them raw. The children gather on the edges of roads and walked chew. They have an acid taste due to the presence of organic acids, particularly oxalic acid, which gives them a certain harshness. Their consumption of too much in its natural state can have adverse effects on health.

A more appropriate use is to boil them and then switch to cold water. They lose their bitterness, but also pleasantly tart flavor.

In winter when the stems begin to die, you pull the rhizomes and are put to dry. They are called kojokon. They are used in traditional medicine to soften the stool and facilitate the evacuation of urine. Young leaves mixed on scratches bleeding stop the bleeding and soothe the pain. Hence the name of the plant itadori. Recipe with shoots (gonpachi prefectures of Wakayama and Kochi): remove the "skin" external shoots of spring mix with salt and saute in the pan. Season with sugar, soy sauce, sake, the rice wine mirin, sesame oil. Sprinkle with shredded bonito and serve.

Recipe with the leaves: boil the young leaves, pass under the cold water, then let them marinate a half day in the sauce for noodles noted by some spices. Then a vegetable and a smooth taste.

During the war, when there were shortages of tobacco leaves were mixed with tobacco leaves itadori.
In India and Southeast Asia, the leaves are used primarily as itadori to roll chewing.

* Medicinal uses in China

The dried rhizome and young leaves of this wild are used as medicine in China. They are enrolled in the Chinese Pharmacopoeia (1999). The rhizome is used as an analgesic, antipyretic, diuretic, expectorant in the treatment of chronic bronchitis, hepatitis, diarrhea, cancer, hypertension, atherosclerosis, vaginal discharge, burns, snake bites.

Nuisances created by the invasion
Regarded as a very decorative plant, it has long been introduced in many gardens and sold by garden centers. Devoid of local predators and competitors, it was very invasive and therefore unfavorable for biodiversity. Its progress is to the detriment of local flora (such as estuaries angelica, Angelica heterocarpa Lloyd, endemic to some estuaries), but also diversity in vertebrates and invertebrates, especially (total abundance decreased on average by about 40 % on the rivers listed, with a number of invertebrate groups decreased from 20 to 30%). This explains that, like other invasive plants, should reduce the wild populations of amphibians, reptiles, and birds and many mammals of riparian habitats because they depend directly or indirectly, the indigenous grass species and / or invertebrates associated for their survival. The wild is common on new soil and degraded environments and poor in biodiversity because of its mode of spread transport of rhizome fragments.

In Europe
Introduced in Europe in the nineteenth century, notably the Netherlands, as an ornamental garden, the Japanese knotweed were naturalized in the late nineteenth century but did not begin their colonization exponentially until the mid-twentieth century. They are spread on land reworked along the roads and railway tracks and along the rivers posing serious environmental problems. Human activities, especially by the movement of contaminated land by rhizomes, in connection with civil works and rural, and floods, which pull these rhizomes (underground stems or green) to the banks, are the basic vectors dispersal of the plant. Because of fertility problems, the dispersal of seeds remains fairly anecdotal.

In Britain, the law prohibits intentionally disperse the plant and requires the eradication of the plant building land.

In France, a law also against introductions, voluntary or not, invasive species (L411-3) but it does at the moment as Jussie.

In North America
It has also been introduced in North America first on the west coast and the east coast of the United States and in 2005 the two waves of colonization have joined within the country. Its progress towards the north east to the north of the St. Lawrence River in Canada was first observed around 1942 in the district of Limoilou of Quebec City. It is now present at the edge of the Canadian boreal forest. Wherever she moved, nothing else will grow. The province of Ontario it a certain size.

The Japanese Knotweed block natural plant succession by preventing the regeneration of other plants by seed or releases. They therefore constitute a real threat to the biological and physical streams, rivers and ripisylve.

Control methods
The methods of combination of preventive measures and eradication or compensatory.

The techniques are all preventive measures to prevent intentional or unintentional dispersal of the plant, or to prevent its establishment on a site (early destruction of the plant before it takes root).

Eradications mechanical techniques
The plant is very difficult to eradicate, especially in growing season, because it is able to repair very quickly (within a few days) its damaged tissues. Tackling the aerial part of the plant (stems and leaves) shall not prevent the survival of the perennial buried in the ground. In addition, the cutting may promote the spread of the plant because the stems are cut bouturent easily. The extraction of the rhizomes is very boring and illusory, as their density in the soil is very important. Moreover, just a piece of rhizome with a bud to regenerate the plant.

It is therefore not yet fully effective mechanical means to eradicate the plant, but trials are underway in France to destroy the underground and perennial plant.

Eradications chemical techniques
Use of chemicals is often complicated (strict conditions of application, followed over several years) and impossible, especially along the rivers and wetlands, herbicides are banned in less than 5 m them.

Compensatory techniques
They include all measures to offset the impacts of the plant, such as plantations, planting and cutting several years to allow other plants to grow. The cutting, however the risk of spreading the plant to other sites, through which stems cut bouturent easily.

Read also