Of all the invasive plant species at Acadia National Park, Japanese Knotweed (Fallopia japonica s.l.) may be the most unique. Imagine a plant that can burst through pavement or sneak in through foundation cracks in your house! Their invasions tend to be sudden and aggressive, making them successful almost globally. They can usually be found in areas that are heavily influenced by human activity, such as roadways, trails, and construction sites. These areas provide it with the large amounts of light that it needs to thrive, and disturbance of the topsoil allows its complex root system to form. Once established, the plant may grow 10 feet in one growing season, making them very easy to spot.

The stalks of Japanese knotweed have been compared to those of bamboo, hollow and segmented, though the plant is actually in the buckwheat (Polygonaceae) family. The leaves are broad, complete, and alternating. The stems tend to take on an orange color once mature, while the leaves are dark green. Each individual stalk flowers at the end of the summer growing season, producing clumps of small, white flowers. After fruit is produced, the stalks are killed off by the first frost of the fall season, however they quickly return from rhizomes below them come spring.

Japanese knotweed grows in dense stands and reaches incredible heights very quickly. This makes it almost impossible for herbivores to feed on or trample it to keep it under control. Its roots are also incredibly hardy and the only way to permanently remove a stand of Japanese knotweed is to completely dig out and remove its rhizomes, a nearly impossible feat. In addition, its fruits are very small and easily spread by waterways and the wind. It is often still planted in gardens by those who are unaware of the damage it can cause, making management a continuous battle.

Like most invasive species, Japanese knotweed is detrimental to its surrounding environment. Although it can appear self-contained at first glance, it is an ever-expanding issue. Growth of new stands blocks out sunlight for native plants below, and since the weed must grow very quickly to do this, it consumes large amounts of minerals and nutrients from the soil. This limits the resources available to nearby species, wiping them out. All this limits biodiversity, which is one of the main reasons that Japanese knotweed is so undesirable within the park.

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