Concept
Reynoutria japonica, synonyms Fallopia japonica and Polygonum cuspidatum, is a species of herbaceous perennial plant in the knotweed and buckwheat family Polygonaceae. Common names include Japanese knotweed and Asian knotweed. It is native to East Asia in Japan, China and Korea. In North America and Europe, the species has successfully established itself in numerous habitats, and is classified as a pest and invasive species in several countries. The flowers are small, cream or white, produced in erect racemes long in late summer and early autumn. Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not related. While stems may reach a maximum height of each growing season, it is typical to see much smaller plants in places where they sprout through cracks in the pavement or are repeatedly cut down. The leaves are broad oval with a truncated base, long and broad, with an entire margin. New leaves of Reynoutria japonica are dark red and long; young leaves are green and rolled back with dark red veins; leaves are green and shaped like a heart flattened at the base, or a shield, and are usually around long. Mature R. japonica forms , dense thickets. Leaves shoot from the stem nodes alternately in a zigzag pattern. Plants that are immature or affected by mowing and other restrictions have much thinner and shorter stems than mature stands, and are not hollow. Identification of Japanese knotweed may be confused with other plants suspected of being knotweed, due often to the similar appearance of leaves and stems. Dogwood, lilac, houttuynia (Houttuynia cordata), ornamental bistorts such as red bistort (Persicaria amplexicaulis), lesser knotweed (Koenigia campanulata), Himalayan balsam (Impatiens glandulifera), broad-leaved dock (Rumex obtusifolius), bindweed (Convolvulus arvensis), bamboo, Himalayan honeysuckle (Leycesteria formosa), and Russian vine (Fallopia baldschuanica) have been suspected of being Reynoutria japonica.
