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Reynoutria japonica - Houtt.

Common Name Japanese knotweed.
Family Polygonaceae
USDA hardiness 4-8
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[238].
Habitats Cold to warm temperate. It grows in forests and humid areas. It grows in wetlands.
Range Origin: Asia.
Edibility Rating    (3 of 5)
Other Uses    (3 of 5)
Weed Potential Yes
Medicinal Rating    (3 of 5)
Care
Fully Hardy Moist Soil Semi-shade Full sun
Reynoutria japonica Japanese knotweed.


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Reynoutria japonica Japanese knotweed.
KENPEI wikimedia.org

 

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Summary


Physical Characteristics

 icon of manicon of flower
Reynoutria japonica is a PERENNIAL growing to 2 m (6ft) by 2 m (6ft) at a fast rate.
It is hardy to zone (UK) 5.
Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. Suitable pH: acid, neutral and basic (alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers moist soil.

UK Hardiness Map US Hardiness Map

Synonyms

Fallopia compacta (Hook.f.) G.H.Loos & P.Keil. Fallopia japonica (Houtt.) Ronse Decr. Pleuropterus cuspidatus (Siebold & Zucc.) H.Gross. Pleuropterus zuccarinii (Small) Small. Polygonum compactum Hook.f. Polygonum cuspidatum Siebold & Zucc. Polygonum hachidyoense Makino. Polygonum reynoutria Makino. Polygonum reynoutria f. colorans Makino. Polygonum sieboldii de Vriese ex L.H.Bailey [Illegitimate]. Polygonum zuccarinii Small. Reynoutria compacta (Hook.f.) Nakai. Reynoutria hachidyoensis (Makino) Nakai. Reynoutria hachijoensis Nakai ex Jotani. Reynoutria hastata Nakai ex Ui. Reynoutria henryi Nakai. Reynoutria uzenensis (Honda) Honda. Tiniaria japonica (Houtt.) Hedberg

Habitats

Edible Uses

Edible Parts: Leaves  Root  Seed  Shoots  Stem
Edible Uses:

Edible Portion: Leaves, Shoots, Rhizomes, Roots. Young shoots in spring - cooked. They can be used as an asparagus substitute[55, 62, 116, 1599, 179, 183]. They have an acid flavour and can also be used as a rhubarb substitute in pies, fruit soups, jams etc[183]. Older stems and shoot tips - cooked[62, 159]. They taste like a mild version of rhubarb[K]. 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[183].

Medicinal Uses

Plants For A Future can not take any responsibility for any adverse effects from the use of plants. Always seek advice from a professional before using a plant medicinally.


Possibly may have similar properties to other knotweeds where the root can be antiphlogistic, bechic, depurative, diuretic, emmenagogue, emollient, febrifuge, stomachic and vulnerary[46, 61, 147, 178, 218]. It is also used in the treatment of women's complaints[147]. A decoction is used in the treatment of burn injuries, boils and abscesses, poisonous snakebites, acute hepatitis, appendicitis, traumatic injuries and menstrual irregularities[147]. The leaves can be crushed and applied externally as a poultice to abscesses, cuts etc, whilst the dried roots can be ground into a powder and applied externally[147]. Extracts of the plant have shown antitumour activity[218].

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Other Uses

Carbon Farming Solutions - Industrial Crop: fiber (Crops grown for non-food uses. Industrial crops provide resources in three main categories: materials, chemicals, and energy. Traditional materials include lumber and thatch, paper and cardboard, and textiles) [1-1].

Special Uses

Carbon Farming

Cultivation details

Experimental Crop  Industrial Crop: Fiber  Management: Hay

Climate: cold to warm temperate. Humidty: humid. Carbon Farming Solutions - Cultivation: experimental. Management: hay (Describes the non-destructive management systems that are used in cultivation) [1-1].

Carbon Farming

  • Experimental Crop  Plant breeders are testing these plants to see if they could be domesticated for cultivation, but they are still in an experimental phase. Examples include milkweed and leafy spurge.
  • Industrial Crop: Fiber  Clothing, rugs, sheets, blankets etc. Currently, almost none of our fiber are produced from perennial crops but could be!
  • Management: Hay  Cut to the ground and harvested annually. Non-destructive management systems maintaining the soil organic carbon.

Temperature Converter

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Propagation

Plants can be grown from seeds.

Other Names

If available other names are mentioned here

Asian Knotweed, Japanese Knotweed. Previously known as Fallopia japonica (Houtt.) Ronse Decr. Fleeceflower, Himalayan fleece vine, monkeyweed, monkey fungus, Hancock's curse, elephant ears, pea shooters, donkey rhubarb, sally rhubarb, Japanese bamboo, American bamboo, and Mexican bamboo. In Chinese medicine, it is known as huzhang which translates to "tiger stick".

Found In

Countries where the plant has been found are listed here if the information is available

Native to East Asia in Japan, China and Korea. In North America and Europe, the species has successfully established itself in numerous habitats and is classified as an invasive species in several countries.

Weed Potential

Right plant wrong place. We are currently updating this section. Please note that a plant may be invasive in one area but may not in your area so it’s worth checking.

Knotweed is native to eastern Asia. It is listed by the World Conservation Union as one of the world's worst invasive species and is now a problem weed in parts of Europe and North America.The invasive root system and strong growth can damage concrete foundations, buildings, roads, paving, retaining walls and architectural sites. It can also reduce the carrying capacity of waterways.

Conservation Status

IUCN Red List of Threatened Plants Status : This taxon has not yet been assessed

Related Plants
Latin NameCommon NameHabitHeightHardinessGrowthSoilShadeMoistureEdibleMedicinalOther

 

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