Native to Japan, this plant came to North America in the 19th century through use as an ornamental plant. Japanese Knotweed is an upright shrub that can reach heights of 10 feet, with broad oval leaves 6 inches long and a couple inches wide. The flowers are very small, green-white and grow in clusters, blooming in the summer. The fruits are winged on three sides. It spreads through seeds but also through vegetative parts of the plant re-sprouting.
Japanese Knotweed has a very high tolerance for poor conditions such as salinity, drought, shade and heat, thus allowing it to compete strongly with native plants. When growing out of control it will form dense thickets that can act to crowd out native species. In the Pacific coastal states and Virginia it is considered a noxious weed. Due to the sprouting ability of vegetative parts of the plant, it can be very hard to control. When roots are small they can be dug up, but more established plants will need a combination of mechanical and chemical means: cutting with application of herbicides.
On the plus side, its young shoots can be cooked and eaten like asparagus, and the seeds are eaten by ground-feeding songbirds.