Knotweed is a non-native, aggressive perennial plant
from Asia in the genus Polygonum that spreads rapidly along waterways by means of
its root/rhizome mass. Pieces of its roots and stems easily wash downstream and take root to form new plants.
Any
stem node or length of rhizome over an inch in length can form a
new plant wherever it is deposited.
There are three kinds of knotweed found in the Clackamas River Basin; Japanese knotweed (Polygonum cuspidatum), giant knotweed (P. sachalinense) and their hybrid, Bohemian knotweed (P. X Bohemica). These three species all have spade to heart-shaped leaves, reddish, hollow stems with nodes similar to bamboo, and delicate white flowers that stand in branches. The difference lies in the height and size of leaf; Japanese knotweed grows to a height of 12 feet and its leaves can be 7 inches long where giant knotweed grows to 15 feet in height and its leaves reach 12 inches in length. The hybrid between these two, Bohemian knotweed, can vary in height and leaf size between the two other species.
Knotweed is harmful to stream side areas because it grows fast and early, an advantage that helps it overgrow and shade out native vegetation.
It will even shade out blackberries!
Knotweed
is relatively new to the Clackamas River Basin (1950s-1960s).
Knotweed must be controlled before it is everywhere, as in
the case of blackberries, English Ivy, and Scotch Broom. It
has not yet reached the level of these other common invasive
and can still be controlled.
Help
us act now to control this invader!
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Polygonum
sp.
Common Names:
Mexican Bamboo
Japanese Bamboo
Japanese Fleece-flower
Japanese Knotweed
Japanese
Knotweed that has overtaken a stretch of bank along the North
Fork of Deep Creek in Boring, OR.
| Sprouts
of Knotweed growing from cut stems swept downstream from
private land: a primary source of Knotweed infestation.
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