Polygonum sachalinense F. Schmidt ex Maxim.
Fallopia sachalinensis (F. Schmidt ex Maxim.) Ronse Decr.
Reynoutria sachalinensis (F. Schmidt ex Maxim.) Nakai
Giant Knotweed, Sakhalin Knotweed, Japanese Bamboo
Giant knotweed is related to the more common and smaller Japanese knotweed. It is Asian in origin, introduced to North America as an ornamental plant. Both knotweeds spread rapidly, and are considered invasive species.
Identification: Giant knotweed favors rivers, swamps, and other wetland regions. They spread via their root systems, which may extend 50 feet or more and have roots up to 3" (7.6 cm) in diameter. Stems are hollow, and thickly clustered, closely resembling bamboo. Plants reach 13' (4 m) in height. Leaves are alternate, ovate (oval, wider at the bottom), cordate (heart-shaped), up to 12" (30 cm) long, with crenate (wavy) edges. Flowers are groups of slender cone-shaped panicles, white or greenish in color, appearing from July to October.
Here is a comparison between giant knotweed and Japanese knotweed:
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|Plant||Stems are hollow, and thickly clustered, closely resembling bamboo. Plants are large, up to 13' (4 m) in height.||Japanese knotweed stems are jointed and hollow like bamboo. Plants reach up to 12' (3.7 m), but are usually half that.|
|Flowers||Groups of slender cone-shaped panicles, white or greenish in color.||In multiple upward pointing spikes containing many tiny white to pale yellow flowers.|
|Leaves||Alternate, ovate (oval, wider at the bottom), cordate (heart-shaped), up to 12" (30 cm) long, with crenate (wavy) edges.||Leaves are oval, wider and flat near the base, 2-6" (5-15 cm) long and 1-4" (2.5-10 cm) wide.|
|Fruit||Triangular, with three “wings.”||Seed pods are shaped like inverted hearts, about ⅛" (3.2 mm) long.|
USDA Zones: 5-8
|Habitats||Rivers, swamps, and other wetland regions.||Wet areas and disturbed areas|
Polygonum sachalinense on Discover Life
Polygonum sachalinense on the King County Washington Noxious Weeds list
Polygonum sachalinense on Wikipedia
Polygonum sachalinense on the USDA Forest Service's Fire Effects Information Database
Polygonum sachalinense on the USDA Plants Database
Polygonum sachalinense on CalPhotos
Polygonum sachalinense on Plants for a Future, a resource and information centre for edible and otherwise useful plants
Polygonum sachalinense description by Thomas H. Kent, last updated 2 Jan 2019.
Range: Zones 5-8: