Alternative common names:
Giant knotweed is an aggressive invader, similar to Japanese knotweed. It is a declared noxious weed in South Africa. It forms dense stands that exclude all other vegetation.
Where does this species come from?Japan and far east of Russia.
What is its invasive status in South Africa?NEMBA Category 1a.
Where in South Africa is it a problem?KwaZulu-Natal.
How does it spread?It is highly invasive, spreading via green plant fragments, rhizome (underground stem) or root fragments.
Why is it a problem?
It has the potential to outcompete and displace indigenous species, particularly in riparian zones (river banks), which it prefers.
It also forms dense thickets of above-ground vegetation, which shades out other species and prevents their regeneration, reducing the biodiversity of invaded areas and altering the habitat available to indigenous animals. Cattle fed on the plant have shown temporary anorexia and hypothermia.
What does it look like?
Giant knotweed is an herbaceous perennial growing to 2-4m tall, with strong, extensively spreading rhizomes forming large clonal colonies (group of genetically identical plants).
Leaves: The leaves are 15-40cm long and 10-28cm wide with deeply heart-shaped bases and blunt leaf tips.
Flowers: The flowers are small, cream or white, and produced in erect racemes 6-15cm long in late summer and early autumn.
Fruit/seeds: The fruit is three-sided, black and shiny.
Does the plant have any uses?
Source of nectar for honeybees; the young stems are edible as a spring vegetable; has medicinal and ornamental purposes.