Japanese Knotweed was originally introduced from Asia as an ornamental and
is still sometimes used in gardens. This highly invasive plant is found along
roadsides and wetland areas where it out-competes native vegetation and is
extremely difficult to control once established. It is known in BC along
roadsides and moist climates especially in the south-west coastal region, but
also in the Shuswap region and the Queen Charlotte Islands.
Biology
Japanese knotweed is a herbaceous, semi-woody perennial member of the
Buckwheat Family. It can grow 3 metres in height. Stems are stout,
reddish-brown, round and hollow forming dense clumps resembling bamboo, giving
rise to its other common names of Japanese and Mexican bamboo. Leathery leaves
are egg-shaped, alternate and form at swollen joints along the stem. They are
10 to 15 cm long, flattened, rounded at the base with a pointed tip and are
dark green above and lighter green below. Plant clumps produce rhizomes, which
can extend 13 - 18 metres in length. Greenish-white flowers bloom in clusters
along the stem, at leaf axils, from August to September.
Reproduction
Primarily reproduction is vegetative through long creeping rhizomes or by
root fragments, which readily produce new plants. Japanese knotweed root pieces
are known to contaminate new sites through movement of dirt. When growing near
water, root fragments can be carried down stream to establish new colonies.
Escapees from deserted gardens are not uncommon.
Habitat
Japanese Knotweed prefers open habitats and does poorly in the under-story
of forested areas. It grows in a variety of soil types along roadsides, edges
of waterways, neglected gardens and unused areas. It is known to grow in
climates experiencing high temperatures and drought. Wetlands and moist,
low-lying areas are the most common habitats.
Concern
Dense stands, capable of crowding out all other vegetation, degrade native
plant communities. It spreads quickly, is extremely aggressive and persistent
and able to survive severe flooding. It poses a significant threat to areas
adjacent to rivers, streams and other shore-lines where it can cause bank
erosion. Clog waterways and lower the quality of habitat for wildlife and fish.
During its dormant growth stages Japanese knotweed dries and can create a fire
hazard.
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![](/web/20061229061349im_/http://www.agf.gov.bc.ca/cropprot/images/jknotweed1.jpg)
Japanese Knotweed - Leaves and Flowers
![](/web/20061229061349im_/http://www.agf.gov.bc.ca/cropprot/images/jknotweed3.jpg)
“Bamboo-like” stems
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