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Japanese Knotweed

Polygonum cuspidatum

Common Name: Japanese Knotweed
Scientific Name: Polygonum cuspidatum
Family: Polygonaceae
Growth Form: Shrub
Native Range: Japan
Invasive Range: The Northeast south to Maryland, and California
Introduction: Japanese knotweed was brought to the U.S. from Japan as an ornamental in the late 1800s.  It subsequently escaped into the wild and thrives in a wide range of habitats including high salinity, shade, and drought.  Spreads using rhizomes, but also produces seeds.
Description: ·Leaves: Alternate and egg-shaped or triangular. 7-15 cm (3-6 in.) long.

·Branches: Smooth and thick.  Hollow like bamboo. Swollen joints where leaf and stem come together.

·Flower: Tiny white flowers in elongated (10-13 cm, 4-5 in.) clusters which come out of leaf axils.  Flowers present in late summer.

·Fruit: Triangular, dark brown seed is enclosed within 3-winged calyx.
Threats: Japanese knotweed grows in impenetrable clumps which shade out all other vegetation and alter native species composition.  It is extrememly difficult to remove once it has taken root. 
Fun Facts: Japanese knotweed has a tangy, tart flavor that has been described as rhubarb-like. (We do not, however, recommend eating it).
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