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Invasive Species Identification Sheet
Japanese Knotweed (Polygonum cuspidatum
Sieb. & Zucc.)
Alternate Latin names: Fallopia japonica
(Houtt.) Ronse Decraene, Reynoutria japonica
Houtt., Pleuropterus zuccarinii Small
Alternate common names: Japanese or Mexican Bamboo, Japanese Fleece-flower;
horticultural varieties include
“Crimson Beauty,” “Variegated” and “compactum”
-perennial, with vigorous, widely-spreading, bushy form; 6'-13' tall; dies back
each year
-stems stout but hollow; ringed with a tubular sheath (ocrea)
at each leaf base with papery remnants encircling the stem even after lower
leaves are shed
-leaves alternate, large (up to 6"-9" long); wide at base, tapering abruptly to
pointed tip
-lacey-white flower sprays emerge in late summer among leaves on upward side of
arched stems
-papery-winged fruits are 3-angled and less than 1/2" long (4 mm –10 mm)
-frost-killed stems turn bronze colored; and may remain upright through winter
Japanese Knotweed and its close relative, the non-native Giant Knotweed (Polygonum
sachalinense F.W. Schmidt ex Maxim.), grow from stout underground
stems (rhizomes) that spread aggressively and send many shoots up causing the
plants to form bamboo-like thickets. Japanese and Giant Knotweed leaves vary in
size and shape. Japanese Knotweed leaves tend to be egg-shaped whereas Giant
Knotweed leaves tend to be longer and can be very large (more than 13" long). In
both species, the smaller leaves have squarish bases while the larger leaves
tend toward heart-shaped bases (more so in Giant Knotweed). The upper surface of
Japanese Knotweed has an extremely fine-sandpaper feel in contrast to the
fine-leather feel of Giant Knotweed.
Japanese Knotweed is spread by seeds and by root fragments that are
transported in fill dirt or by moving water. It sprouts out from below ground in
early Spring and grows rapidly and profusely on roadsides, streambanks, wetland
margins, floodplains, and gravel bars.
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