Japanese knotweed.
Reynoutria japonica
Family: Polygonaceae
What it is like
Reynoutria japonica is a PERENNIAL growing to 2 m (6ft) by 2 m (6ft) at a fast rate. See above for USDA hardiness. It is hardy to UK zone 5. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers moist soil.
Height (m): 2
Where it is found
Cold to warm temperate. It grows in forests and humid areas. It grows in wetlands.
Origin: Asia.
Conservation Status: This taxon has not yet been assessed
Countries/locations it is found in
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.
How it is used
Food
Rating: 3
Edible Portion: Leaves, Shoots, Rhizomes, Roots. 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.
Root: includes bulbs, corms, tubers, rhizomes etc.
Seed: includes nuts, cereals, peas and beans.
Stem: this often intergrades into leaves.
Medicine
Rating: 3
Possibly may have similar properties to other knotweeds where the root can be antiphlogistic, bechic, depurative, diuretic, emmenagogue, emollient, febrifuge, stomachic and vulnerary. It is also used in the treatment of women's complaints. A decoction is used in the treatment of burn injuries, boils and abscesses, poisonous snakebites, acute hepatitis, appendicitis, traumatic injuries and menstrual irregularities. 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. Extracts of the plant have shown antitumour activity.
Other
Rating: 3
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).
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.
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.
Carbon Farming: Plants that can be a critical part of the solution to climate problems. The Carbon Farming Solution - Eric Toensmeier.
Food Forest: Plants for Edible Forest Gardens and Food Forests.
How it is grown
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). In garden design, as well as the above-ground architecture of a plant, root structure considerations help in choosing plants that work together for their optimal soil requirements including nutrients and water. The root pattern is rhizomatous with underground stems sending roots and shoots along their length .
Propagating it: Plants can be grown from seeds.
Best place to grow:
Habit: Perennial
Hardiness: 4-8
Growth: Fast
Soil: Light (sandy), medium, heavy (clay)
Shade: Semi-shade, no shade
Moisture: Moist
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.
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.
Its other names
Local names
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".
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