Polygonum cuspidatum Siebold & Zucc.
Fallopia japonica (Houtt.) Ronse Decr.
Pleuropterus cuspidatus (Siebold & Zucc.) Moldenke
Pleuropterus zuccarinii (Small) Small
Polygonum cuspidatum Siebold & Zucc. var. compactum (Hook. f.) L.H. Bailey
Polygonum zuccarinii Small
Reynoutria japonica Houtt.
Japanese knotweed, Mexican bamboo
Another story of a good plant gone bad. Japanese knotweed is a native of Japan, China, and Korea. Introduced to Europe and North America as an ornamental plant, it has been so successful that it is considered one of the 100 worst invasive species. Fast-growing root systems form dense hedges that crowd out other species.
Identification: Japanese knotweed stems are jointed and hollow like bamboo. Thin branches are reddish. Plants reach up to 12' (3.7 m). Flowers appear in multiple upward pointing spikes containing many tiny white to pale yellow flowers. Leaves are oval, wider near the base, 2-6" (5-15 cm) long and 1-4" (2.5-10 cm) wide. Seed pods are shaped like inverted hearts, about ⅛" (3.2 mm) long. The plants favor wet areas and disturbed areas.
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|
Medical: Historically, extracts from Japanese knotweed have been used to treat menstrual cramps and postpartum depression. Other ingredients aid in treatment of burns; these are also used in skin lotions. There are many other purported but unconfirmed health benefits.
Edibility: Thicker young shoots, gathered early in the spring, can be cooked in boiling water or a steamer and served with butter, like asparagus. And like asparagus, they cook quickly, and should be served as soon as they are easily pricked with a fork. See herbalpedia.
Polygonum cuspidatum on Wikipedia
Polygonum cuspidatum at the Washington State Department of Ecology
Polygonum cuspidatum on www.ag.purdue.edu (PDF)
Polygonum cuspidatum on Invasive.org, Center for Invasive Species and Ecosystem Health
Polygonum cuspidatum on spes.vt.edu
Polygonum cuspidatum on CalPhotos
Polygonum cuspidatum on klemow.wilkes.edu (a technical summary of the medical properties)
Polygonum cuspidatum description by Thomas H. Kent, last updated 25 May 2020.