The figurative and literal roots of Japanese knotweed lie (unsurprisingly) in Japan and Southeast Asia, where it has grown for thousands of years. Its range was limited to this area until the age of European exploration, when intercontinental travel and trade became common. The plant's small seeds could easily become attached to sailors' clothes or goods, allowing for their accidental distribution at port cities across the world. Japanese knotweed, already predisposed to rainy, mild climates, was easily able to grow in these locations. Today, its growth is considered problematic in many of them.

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To make matters worse, the plant's spread was not entirely accidental. Some explorers, especially the British, took a liking to the plant because of its attractive flowers and bamboo-like appearance. The plant was brought from Asia to England, where it was grown in gardens for decades. Today, England faces more problems due to Japanese knotweed and its excessive growth than any other nation in the world. 

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The map to the right shows the current range of Japanese knotweed in the United States. Its spread in these areas showcases its remarkable ability to thrive in diverse climates.

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