Japanese knotweed is one of the world's worst invasive species. In the centuries since it was first transported out of Southeast Asia, it is known to have established itself in North America, Europe, Oceania, and parts of Asia far outside of its native range. It is possible that it has spread even further, but documented cases only exist in those locations. 

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The qualities of Japanese knotweed that have allowed it to spread so pervasively are worth noting. It is a remarkably versatile plant, able to grow and thrive in a wide range of conditions. Unfortunately, the plant also grows more aggressively than almost all others on the planet (in warm, sunny areas, mature knotweed plants can grow at the blistering rate of four inches in height per day). This combination of adaptations allows the plant to dominate almost any ecosystem by limiting other organisms' abilities to obtain nutrients, both from the sun and the soil. It is known for easily overpowering plants in their native ranges, and its victims include everything from vines to brush to small trees. The plant's density of growth also aids it in its conquests- its tightly packed stems and leaves create thick 'canopies,' nearly impenetrable by sunlight. Plants caught underneath these growths are almost always killed due to a lack of light.

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The plant is almost as oppressive under the ground as it is above it. Its extensive root and rhizome systems take in large quantities of nutrients from soil, leaving little for other plants. Again, this often results in the deaths of plants trying to grow near the knotweed.

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Outside of its native range, the plant has very few effective predators. Its growth usually occurs unchallenged in the areas it invades.

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The plant is capable of causing economic problems in addition to ecological ones. In some places, the plant has become notorious for damaging manmade structures. Its rhizomes are capable of growing into roads, building foundations, and other structures not usually damaged by plants.

 

The country most dramatically afflicted by this invasive plant is undoubtedly England. Huge investments have been made there to control the plant's growth with limited success. Laws have also been put in place mandating that property owners attempt to control knotweed growth on their land. Failure to abide by the law can result in hefty fines. This measure has been quite controversial because of the way in which it has impacted the English housing market- many prospective homeowners are not purchasing houses near knotweed growth, leaving owners of properties that contain knotweed unable to sell their land. The convolution of this situation serves as an example of the damage that knotweed can cause in the areas it invades.