Cemre Kara, Hyunsuh Kim

Japanese Knotweed: Rethinking Invasive Species

Around the mid-1800s, botanical interests in Europe were high. Searching for beautiful unique plants around the world, for study purposes, or using them as ornamentals was common practice. So much that many species were being shipped from their natural habitats to Kew Gardens, nurseries, and gardens in Europe and North America.


26-03-2020 Japanese Knotweed - 6 knoppen van de Japanse Duizenknopp - De Japanse duizendknoop is voor Amsterdam een lastpak. De struik lijkt elke winter te verdwijnen maar in het voorjaar komt het weer groter en sterker terug. Het ziet er prachtig uit boven de grond maar eronder is het een woekeraar. Zo erg dat het schade brengt aan niet alleen andere planten maar ook: kabels, rioolbuizen, funderingen en muren! MediaMatic zag een kans om van een pest iets moois te maken. De knoppen van de struik zijn fantastisch om mee te koken.  Deze knoppen van de jonge onkruid… Willem Velthoven

Originally described as Reynoutria Japonica by Houttuyn in 1777 from Japan introduced to the West in mid 19th century by the famous Bavarian physician, botanist Philippe von Siebold who first discovered the species growing in near Nagasaki, on the side of the volcanoes.

In the 1840s it was shipped from Japan, along with other types of plants to Philippe von Siebold’s nursery, in Leiden, Holland.

The beauty of this particular species attracted so many people’s attention that the plant was even named as the ‘the most interesting new ornamental plant of the year’ in 1847, by the Society of Agriculture and Horticulture in Utrecht. In 1850, specimens of the plant were already sent to the Royal Botanical Gardens at Kew (UK).

It’s “pretty heart-shaped leaves, white flower and its growth” was remarkable to the people of the time. It even conquered the favor of Victorian Gardeners. So much that soon enough many gardens in the UK enthusiastically shared the plant with each other.

However, the glory days of our plant went away quickly after it was proved to be invasive and destructive. The growth was so fast that it was almost impossible to stop.

And just like that, this species was no longer desired.

By 1901, Makino, a Japanese botanist, realized Houttuyn ’s Reynoutria Japonica, and what we call Japanese Knotweed are the same specıes, scientifically known as Fallopia Japonica.

It is said that this pretty looking plant is now the most unwanted and invasive plant in Europe.

Trapped in a foreign land, a great amount of money has been spent trying to control the outbreak of the species. As a matter of fact, in 2012 during the building of the Olympic Park in East London, the government spent £70 million alone to clear the Japanese Knotweed from the site. 


How does Japanese Knotweed behave in its natural habitat?

In its natural habitat (East Asia; Korea, and China and mainly in Japan) Japanese knotweed grows on the side of the volcanoes, in extreme climates. There, the native insects and fungi limit the plant from spreading more.

For centuries, it was used in agriculture, bee-keeping activities, medicine, culinary, and as a ceremonial herb. This is mostly because of its positive effects on health. Recent studies suggest that the Japanese Knotweed has benefits for cognitive disorders, like Alzheimer’s disease and dementia. This is because of the resveratrol content of the herb. (resveratrol; plant compound that acts as an antioxidant), this means that resveratrol can keep brain pathways energized and in use. Furthermore, resveratrol has been known to help moderate cholesterol level and blood pressure and thus help prevent heart diseases, in addition to being a mild laxative that can alleviate gastrointestinal symptoms (Staughton). Nevertheless, I should note it is warned that taking an excessive amount of Japanese Knotweed can induce negative reactions, and the dosage of this herb should be under guidelines. Yet the perks of the Japanese Knotweed are greater than it’s downsides. 


How does Japanese Knotweed behave in its "foreign" habitat?

While Japanese Knotweed supports the flourishing of native flora and fauna in its natural habitat, studies have repeatedly found that it can quickly dominate a foreign area and capitalize on resources at the expense of other species in new environmental niches. By competing with resources and allelopathically changing the soil chemistry with its rhizomes, Japanese Knotweed in Europe has a negative impact on biodiversity, particularly in riparian areas, resulting in up to 10 times fewer species in invaded areas (Lavoie; Murrell et al.). By displacing other species of plants by the river bank, the Japanese knotweed also contributes to soil erosion and floods (Colleran et al.). For its rhizomes and stems travel through water, such flooding further reinforces the spread of the plant. Human contribution in forming riverways and canals, illegal dumping of soil, and extreme weather conditions due to climate change have also been considered to accelerate this process. In this sense, the Japanese Knotweed is a countering force to the Dutch aspiration to push the water and continue expanding its land, ironically assisted by the very process of prioritizing human needs in the making of this land. Such dualistic role of the Japanese Knotweed in different contexts — a pioneer in its local environment and an invader in foreign environments —, renders a powerful caveat to the Netherlands that often sees itself as solely a pioneer and in the process fails to sufficiently act upon its colonial history and its ongoing adverse effects. Such recognition is even more poignant to the extent that the Dutch have been actively, albeit unknowingly assisting the proliferation of the octaploid variant of Japanese knotweed from the beginning of its "invasion" to today.


It's edible! 

As we all can assume it would not be suggested to forage them by yourself because of its fast growth. However, with careful foraging techniques, this problem can be solved. We have so many of these plants, we are making them illegal and trying to keep them away from our soil, our gardens with chemical preventions along with the soil. Wouldn’t it be great to actually use them and consume them, or have them in our food markets?

Yes, Japanese Knotweed is in the highest list of invading species in Europe. However with climate change, that humans created, it is getting hard to recognize what is a native and what is an invader. An article that I recently read about the topic “Invasive Plants And Invasion Biology As Destructive Concepts” gave me another perspective to look at the situation. 

When plants and animals are moving towards different locations in search of conditions they can tolerate, we can’t deny that the Earth is changing and it is not stable.

We should also not forget that humans fasten the phase of change, bringing these plants from their natural habitats. We’ve done this while systematically destroying ecosystems and wild areas. Seeing nature as something stable. I came across the following phrase that was very fitting:

"Evolution is about adaptation and change; our fossil records show that throughout the many millennia of earth’s existence, the only constant is change and the ability to adapt.

This is a natural process and one that has driven all life. We are already seeing the effects of climate change with the migration of species to areas that are now getting warmer. Nature will adapt and evolve, it’s just what she does. "

So maybe it is time to give this species another chance before we call them invaders, or at the very least, recognize the complexity of the histories and contexts in which such labels form, and enjoy the perks of the plant that we have in abundance in our cities.


Illustration by Mattia Papp of Japanese Knotweed -


Illustrated by Mattia Papp -



Colleran, Brian; Lacy, Shaw Nozaki; Retamal, Maria Rafaela. (2020). “Invasive Japanese knotweed (Reynoutria japonica Houtt.) and related knotweeds as catalysts for streambank erosion”. River Research and Applications 36(9): 1962-1969. doi:10.1002/rra.3725

“History of Japanese Knotweed in Europe.” University of Leicester, 7 Oct. 2009, www2.le.ac.uk/departments/genetics/people/bailey/res/hist.

Haan, Gemeente Amsterdam Klaas-Bindert de. “Zoom in for the Contours Ofthe Viewed Growing Places.” Knotweed, maps.amsterdam.nl/duizendknoop/?LANG=en.

“Invasive Plants and Invasion Biology as Destructive Concepts: A Druid's Perspective.” The Druid's Garden, 9 Oct. 2014, druidgarden.wordpress.com/2014/10/09/invasive-plants-and-invasion-biology-as-destructive-concepts-a-druids-perspective/.

Jennings, Kerri-Ann. “7 Health Benefits of Resveratrol Supplements.” Healthline, Healthline Media, 3 Mar. 2017, www.healthline.com/nutrition/resveratrol.

Lavoie, C. “The impact of invasive knotweed species (Reynoutria spp.) on the environment: review and research perspectives”. Biological Invasions 19, 2319–2337 (2017). https://doi-org.proxy.uba.uva.nl:2443/10.1007/s10530-017-1444-y

Murrell, Craig, Esther Gerber, Christine Krebs, Madalin Parepa, Urs Schaffner, and Oliver Bossdorf. "Invasive Knotweed Affects Native Plants through Allelopathy." American Journal of Botany 98, no. 1 (2011): 38-43. Accessed April 15, 2021. http://www.jstor.org/stable/25766887.

Rob. “Benefits of Japanese Knotweed.” Taylor Total Weed Control, 2 Sept. 2019, www.taylor-weed-control.co.uk/news/post/health-benefits-of-japanese-knotweed.

Staughton, John. "Top 7 Benefits of Japanese Knotweed".Organic Facts, 29 Jan. 2020. https://www.organicfacts.net/health-benefits/herbs-and-spices/japanese-knotweed.html?fbclid=IwAR0K4BLRZ-HCFPeJoKisOS6BC-yU6o0nUkRVG2z1CytYiLpwhJ5vOsKL70Y

What Does Japanese Knotweed Look Like? - Knotweed Specialists.” Japanese Knotweed Specialists, japaneseknotweedspecialists.com/what-is-japanese-knotweed/.