Photo courtesy Mike Carter, Pensacola, Florida
Japanese Knotweed is one of the most invasive weeds in
the world. In Asia it is regarded as having medicinal value,
and as such was introduced to North America in the 1870s as an
ornamental and forage plant, but its extracts were never put
to test as a medicinal herb. It is difficult to exaggerate how
aggressive this species can be, as it has been observed growing
through two inches of concrete, and it will regenerate from the
smallest section of root tissue. Control of Japanese knotweed
is laborious and expensive. Its preferred habitat is floodplains
(river or stream floodplains), forest edges, meadows and fields,
and the shores of rivers and lakes.
The leaves are simple (i.e., lobed or unlobed but not separated
into leaflets); placed alternate on the stem. The leaf blade
is entire (no teeth and no lobes).
The flowers are radially symmetrical; five petals, sepals,
or tepals in each flower. Fusion of sepals and petals form a
small cup or tube; eight stamens. Flowers in August and September.
Fruit is a capsule that does not split open when ripe.