Appearance
Identification of Japanese knotweed is not always easy. Many other plants are suspected of being knotweed, due often to the similar appearance of leaves and stems. Dogwood, lilac, Houttuynia , ornamental Bistorts such as Red Bistort '', lesser knotweed , Himalayan Balsam , Broadleaved Dock , Bindweed , bamboo, Himalayan Honeysuckle , and Russian Vine have been suspected of being ''Reynoutria japonica''.New leaves of ''Reynoutria japonica'' are dark red and 1 to 4 cm 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 12 cm long. Mature ''R. japonica'' forms 2-to-3-metre tall dense thickets; stems look somewhat like bamboo, with rings and purple speckles. Leaves shoot from the stem nodes alternately in a zigzag pattern. Mature stems are hollow and not at all woody: they can be snapped easily to see if they are hollow. Plants that are immature or affected by mowing or other restrictions have much thinner and shorter stems than mature stands, and are not hollow.
Naming
It is listed by the World Conservation Union as one of the world's worst invasive species.The invasive root system and strong growth can damage concrete foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites. It can also reduce the capacity of channels in flood defences to carry water.
It is a frequent colonizer of temperate riparian ecosystems, roadsides and waste places. It forms thick, dense colonies that completely crowd out any other herbaceous species and is now considered one of the worst invasive exotics in parts of the eastern United States. The success of the species has been partially attributed to its tolerance of a very wide range of soil types, pH and salinity. Its rhizomes can survive temperatures of −35 °C and can extend 7 metres horizontally and 3 metres deep, making removal by excavation extremely difficult. The plant is also resilient to cutting, vigorously resprouting from the roots.
Uses
Japanese knotweed flowers are valued by some beekeepers as an important source of nectar for honeybees, at a time of year when little else is flowering. Japanese knotweed yields a monofloral honey, usually called ''bamboo honey'' by northeastern U.S. beekeepers, like a mild-flavoured version of buckwheat honey .The young stems are edible as a spring vegetable, with a flavour similar to extremely sour rhubarb. In some locations, semi-cultivating Japanese knotweed for food has been used as a means of controlling knotweed populations that invade sensitive wetland areas and drive out the native vegetation. It is eaten in Japan as ''sansai'' or wild foraged vegetable.
It is used in traditional Chinese and Japanese medicine to treat various disorders through the actions of resveratrol, although there is no high-quality evidence from clinical research for any medical efficacy. Extracts of resveratrol from ''R. japonica'' roots are higher in content than those from stems or leaves, and have highest levels at the end of the growing season.
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