About Reynoutria compacta (Hook.fil.) Nakai
This description covers characteristics of the Reynoutria compacta group, including traits shared with related Japanese knotweed (Reynoutria japonica). The small cream or white flowers are produced in erect racemes 6–15 cm (2+1⁄2–6 in) long, blooming in late summer and early autumn. Japanese knotweed typically has hollow stems with distinct raised nodes that give it a bamboo-like appearance, though it is not related to bamboo. Stems reach a maximum height of 3–4 m (10–13 ft) each growing season, but plants growing through pavement cracks or repeatedly cut down are usually much smaller. For R. japonica, new leaves are dark red and 1 to 4 cm (1⁄2 to 1+1⁄2 in) long; young leaves are green, rolled back, and have dark red veins. Mature leaves are green, shaped like a heart flattened at the base or a shield, and usually around 12 cm (5 in) long. Leaves of mature plants are broad oval with a truncated base, 7–14 cm (3–5+1⁄2 in) long and 5–12 cm (2–4+1⁄2 in) broad, with an entire margin. Leaves grow from stem nodes alternately in a zigzag pattern. Mature R. japonica forms dense thickets 2–3 metres (6+1⁄2 to 10 ft) tall. Immature plants or plants repeatedly damaged by mowing or other restrictions have much thinner, shorter stems that are not hollow. This species is native to East Asia, specifically Japan, China and Korea. It has become successfully established in numerous habitats across North America and Europe, and is classified as a pest and invasive species in several countries. Some beekeepers value Japanese knotweed flowers as an important nectar source for honeybees, as they bloom at a time of year when few other plants flower. Japanese knotweed produces a monofloral honey, usually called bamboo honey by beekeepers in the northeastern United States. This honey has a mild flavour similar to that of buckwheat honey; buckwheat is a related plant also in the Polygonaceae family. The young stems of Japanese knotweed are edible as a spring vegetable, with a flavour similar to rhubarb. In some locations, semi-cultivating Japanese knotweed for food has been used as a method to control knotweed populations that invade sensitive wetland areas and outcompete native vegetation. It is eaten as sansai, a wild foraged vegetable, in Japan. Young shoots are also used in restaurant cuisine in Europe. Knotweed can grow up to 30 cm per day, making it a fast-growing vegetable that tolerates poor quality soils. Because it is resistant to over-harvesting, it is more often foraged than cultivated as a vegetable. The plant can be eaten either raw or cooked. Ground-feeding songbirds and gamebirds also eat its seeds.
