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Japanese Knotweed

Fallopia japonica

Please keep in mind that it is illegal to uproot a plant without the landowner's consent and care should be taken at all times not to damage wild plants. Wild plants should never be picked for pleasure and some plants are protected by law.
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Plant Profile
Similar Species
Other Information
Distribution Map

Flowering Months:

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Order:

Caryophyllales

Family:

Polygonaceae (Dock)

Also in this family:

Alpine Bistort, Amphibious Bistort, Argentine Dock, Black Bindweed, Broad-leaved Dock, Clustered Dock, Common Bistort, Common Buckwheat, Common Knotgrass, Common Sorrel, Copse Bindweed, Cornfield Knotgrass, Curled Dock, Equal-leaved Knotgrass, Fiddle Dock, French Sorrel, Garden Rhubarb, Giant Knotweed, Golden Dock, Greek Dock, Himalayan Knotweed, Iceland Purslane, Least Water-pepper, Lesser Knotweed, Marsh Dock, Monk's Rhubarb, Mountain Sorrel, Northern Dock, Northern Knotgrass, Pale Persicaria, Patience Dock, Pink Knotweed, Ray's Knotgrass, Red Bistort, Redleg, Russian Vine, Scottish Dock, Sea Knotgrass, Sheep Sorrel, Shore Dock, Tasteless Water-pepper, Water Dock, Water-pepper, Wood Dock

Type:

Flower

Life Cycle:

Perennial

Maximum Size:

4 metres tall

Habitats:

Disturbed ground, fields, meadows, riverbanks, riversides, roadsides, towns, waterside, wetland, woodland.

Flower:

✿

White, 5 petals

Japanese Knotweed produces dense clusters of small, creamy-white flowers in late summer, typically between August and September. These flowers emerge from the upper leaf axils and form delicate sprays, giving the plant a frothy appearance when in bloom. Although individually small, the abundance of blossoms makes the flowering stems visually striking and highly attractive to pollinators such as bees.

Fruit:

While Japanese Knotweed does produce small, winged fruits known as achenes, these are rarely viable in the UK because most plants are female clones and lack genetic diversity. Reproduction here is almost exclusively vegetative, through its extensive rhizome (underground stem) system, which enables the plant to spread rapidly and regenerate from even tiny root fragments.

Leaves:

The leaves are broad, shield- or heart-shaped with a flat base and pointed tip, measuring around 10–15 cm long. They grow in a zigzag pattern along hollow, bamboo-like stems, which can reach up to 3 metres tall. The leaves are lush green during the growing season and turn yellow in autumn before the plant dies back above ground.

Fragrance:

Japanese Knotweed has little to no fragrance. Its flowers may emit a faintly sweet scent detectable to insects but are not noticeably aromatic to humans. The leaves and stems are also unscented, even when crushed.

Other Names:

American Bamboo, Asian Knotweed, Asiatic Knotweed, Bombascus, Donkey Rhubarb, Elephant Ear's, False Bamboo, Fleeceflower, Gypsy Rhubarb, Hancock's Curse, Himalayan Fleece Vine, Itadori, Japanese Bamboo, Japanese Fleeceflower, Japanese Polygonum, Kontiki Bamboo, Mexican Bamboo, Monkey Fungus, Monkeyweed, Pea Shooters, Sally Rhubarb.

Frequency (UK):

Common

Giant Knotweed

Himalayan Knotweed

Lesser Knotweed

Summary

Fallopia japonica, also known as Japanese knotweed, is an invasive perennial plant species in the buckwheat family (Polygonaceae). It is native to Japan, China and Korea, but has been introduced to many other parts of the world, where it can be found growing in a wide range of habitats, including riverbanks, roadsides, and waste ground. It can grow up to 10 feet tall, with bamboo-like stems, large green leaves, and small white or pink flowers that bloom in late summer. It is considered a highly invasive species due to its ability to outcompete native plants, and its ability to grow through concrete and asphalt. It can be difficult to control and remove once established.

Blog

Japanese Knotweed, also known as Fallopia japonica, is a perennial plant that is native to Eastern Asia, including Japan, Korea, and China. It is a member of the Polygonaceae family and is considered one of the most invasive plant species in the world. It is classified as an invasive species in many countries, including the United States, Canada, and the United Kingdom, where it is considered a significant threat to native ecosystems.

Identification and Characteristics

Japanese Knotweed can grow up to 3-4 meters tall and has large, heart-shaped leaves that are about 10-20 cm long. Its stems are hollow and bamboo-like, with distinct raised nodes that are spaced about 10-20 cm apart. The plant also produces clusters of small, white or cream-colored flowers that bloom in late summer and early autumn.

Habitat and Distribution

Japanese Knotweed prefers moist, well-drained soils and can grow in a wide range of habitats, including riverbanks, roadways, and waste areas. It is tolerant of shade and can grow in both full sun and partial shade. The plant is native to Eastern Asia, but it has been introduced to many other parts of the world, including Europe, North America, and New Zealand.

Impacts on Ecosystems and Biodiversity

Japanese Knotweed is considered a major threat to biodiversity because it can rapidly outcompete and displace native plant species. It forms dense stands that shade out other plants and can alter soil chemistry, which can further inhibit the growth of native species. This can have cascading effects on local ecosystems, including changes in the availability of food and habitat for wildlife.

In addition to its impacts on native biodiversity, Japanese Knotweed can also have significant economic impacts. Its ability to grow through concrete and asphalt can damage roads, buildings, and other infrastructure, resulting in costly repairs.

Control and Management

Due to its invasive nature, Japanese Knotweed can be challenging to control and manage. Traditional control methods such as cutting, burning, and herbicide application have shown limited effectiveness. Effective management strategies typically involve a combination of methods, including physical removal, herbicide application, and ongoing monitoring.

Prevention is also critical in controlling the spread of Japanese Knotweed. Avoiding planting the species in gardens and other landscaped areas can help prevent its introduction, and early detection and rapid response can help prevent the establishment and spread of new infestations.

Japanese Knotweed is a highly invasive plant species that poses significant threats to native ecosystems and biodiversity. Effective management strategies involve a combination of methods and prevention is critical in controlling its spread. Awareness and action are needed to help prevent the continued spread and negative impacts of this invasive plant.

Ethnobotanical uses

While Japanese Knotweed is considered an invasive species in many parts of the world, it has been traditionally used in Eastern Asia for a variety of medicinal purposes. It has been used in traditional Chinese medicine to treat conditions such as menstrual irregularities, respiratory infections, and gastrointestinal issues. In Japan, the plant is used to make a sweet syrup called "kuzuyu," which is used as a natural remedy for colds and coughs. However, it is important to note that the efficacy and safety of using Japanese Knotweed for medicinal purposes have not been scientifically proven.

Legal considerations

In many countries, including the United States and the United Kingdom, Japanese Knotweed is considered a "controlled waste" and must be disposed of properly. It is illegal to intentionally plant or allow the plant to spread in the wild. Property owners who fail to control the spread of Japanese Knotweed can be held liable for damage caused to nearby properties.

Public awareness and education

Public awareness and education about the impacts of Japanese Knotweed are critical in preventing its spread and mitigating its negative impacts. This can involve educating homeowners, landscapers, and other professionals about how to identify and manage the plant, as well as raising awareness about the importance of preventing its spread through activities such as cleaning equipment and disposing of plant materials properly.

Efforts to raise public awareness about Japanese Knotweed have been successful in many parts of the world. For example, in the United Kingdom, there is a national "PlantTracker" app that allows users to report sightings of invasive species, including Japanese Knotweed. This helps authorities to track the spread of the plant and respond quickly to new infestations.

Research and ongoing efforts to control Japanese Knotweed

Scientists and land managers are continuously working to find new and effective ways to control and manage Japanese Knotweed. This can involve testing new herbicides, exploring biological control options (such as introducing natural predators or pathogens), or experimenting with innovative management strategies such as using drones to map infestations.

Alternative uses for Japanese Knotweed

In addition to its traditional medicinal uses, Japanese Knotweed has potential as a food source and as a material for producing renewable energy. The young shoots of the plant can be eaten as a vegetable, and research has shown that the plant has high levels of resveratrol, a compound with potential health benefits. The plant's large biomass also makes it a potential feedstock for producing biofuels.

The role of climate change in the spread of Japanese Knotweed

Climate change is thought to be contributing to the spread of invasive species, including Japanese Knotweed. Rising temperatures and changing precipitation patterns can create more favorable conditions for the plant to thrive, while also making it more difficult to control through traditional management strategies. Understanding the role of climate change in the spread of Japanese Knotweed is important for developing effective management strategies and mitigating its impacts.

Facts about Japanese Knotweed

Here are some facts about Japanese Knotweed:

Japanese Knotweed (Fallopia japonica) is a highly invasive plant species that is native to eastern Asia.
It was introduced to Europe and North America in the 19th century as an ornamental plant, but it has since become a significant environmental problem in many countries.
Japanese Knotweed can grow up to 3-4 meters (10-13 feet) tall and has distinctive bamboo-like stems that are green with purple speckles.
The leaves are large and heart-shaped, and the plant produces clusters of small, white or cream-colored flowers in late summer or early fall.
Japanese Knotweed spreads quickly and aggressively through its extensive root system, which can grow up to 3 meters (10 feet) deep and 7 meters (23 feet) wide.
The plant can survive in a wide range of environments and soil types, and is able to grow in areas with poor soil quality, high salinity, and even on steep slopes.
Japanese Knotweed is extremely difficult to control or eradicate once it has become established, as even small fragments of the plant's roots or stems can grow into new plants.
The plant is known to damage infrastructure, including building foundations, roads, and drainage systems, and can cause significant environmental damage by outcompeting native plant species and reducing biodiversity.
Japanese Knotweed is listed as a prohibited plant in many countries, including the United States and the United Kingdom, and its removal and disposal is subject to strict regulations.
There are various methods of controlling Japanese Knotweed, including chemical treatments, physical removal, and burying the plant's roots under impermeable barriers, but eradication can take many years and may not be entirely successful.

Video

Japanese Knotweed filmed in Chorley, Lancashire on the 3rd September 2022.

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Reproduced by kind permission of the BSBI.

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