COMMON NAME

Giant knotweed
Sakhalin knotweed


FULL SCIENTIFIC NAME

Polygonum sachalinense F. Schmidt ex Maxim.


FAMILY NAME COMMON

Knotweed family


FAMILY SCIENTIFIC NAME

Polygonum sachalinense


IMAGES


Habit

Leaves

Flowers

Leaf size

Comparison of leaves of P. sachalinense (right of each pair) and P. cuspidatum

NOMENCLATURE/SYNONYMS

Synonyms: Fallopia sachalinensis (F. Schmidt ex Maxim.) Dcne.
Reynoutria sachalinensis (F. Schmidt ex Maxim.) Nakai


DESCRIPTION

Polygonum sachalinense is an herbaceous perennial that is woody in appearance and can grow over 3 meters tall (9.8 ft.). It has erect stems that are hollow, glabrous, jointed, swollen at the nodes and often arched over near the top of the plant. The twigs often appear to zigzag from node to node. The leaves are alternate, petioled and 15-35 cm (6-14 in.) in length. The shape of the leaf is ovate (sometimes lanceolate) with a gradually tapering tip, a heart shaped base and rounded basal lobes. The flowers are borne in numerous axillary panicles found mainly on the upper stems of the plant. The panicles are open, and grow up to 10 cm (3.9 in.) in length. The flowers are functionally unisexual; each male and female flower still has the complementary organs, but these are vestigial. The flowers have five sepals and no petals. The sepals of the male flowers are greenish and 6-7 mm (0.23-0.28 in.) in length. The sepals of the female flowers are more greenish - white and 12-15 mm (0.47-0.59 in.) in length. The fruits are papery, broadly winged (three wings from persisting outer sepals), and 12-15 mm (0.47-0.59 in.) in length. Each fruit contains a three-sided achene that is shiny, brown, ovoid in shape, and 2-4 mm (0.08-0.16 in.) in length. The flowers of Polygonum sachalinense appear from August to October. During a frost, Polygonum sachalinense plants quickly turn a reddish-brown and die back to the ground, although some dead stems may remain standing through the winter. Page References Bailey 384, Fernald 589, Gleason & Cronquist 139, Holmgren 124, Magee & Ahles 441, Seymour 236. See reference section below for full citations.


SIMILAR SPECIES

Polygonum cuspidatum (Japanese knotweed)
Polygonum x bohemica (hybrid cross between P. sachalinense and P. cuspidatum) These three species can look very similar to each other. The most reliable character for distinguishing them is the type of hair on the veins of the leaf undersides, which can be seen with the aid of a strong hand lens.


REPRODUCTIVE/DISPERSAL MECHANISMS

Polygonum sachalinense spreads primarily by its rhizomes. The rhizomes can be dispersed by natural causes, such as flooding and erosion, and also by anthropogenic disturbances to the soil. Polygonum sachalinense produces only small amounts of viable seed. These seeds are mainly dispersed by gravity, wind and water.


DISTRIBUTION

Polygonum sachalinense is native to Japan and the Sakhalin and Kuril islands of Russia. The USDA Plants Database reports that it is present in all of the northeastern U.S. with the exception of New Hampshire, South to North Carolina and Tennessee and west to Minnesota. It has also been reported in Lousianna, Montana, Idaho, Alaska, and the three west coast states.


HISTORY OF INTRODUCTION IN NEW ENGLAND

Polygonum sachalinense was first introduced to the United States from Japan as a garden ornamental in 1894. It may also have been introduced for use as a forage plant. Herbarium specimens at the University of Connecticut noting its escape and spread in Connecticut, Rhode Island and Massachusetts begin in the 1920's and 1930's. In comparing it to Polygonum cuspidatum, Fernald (1950) stated that it was "similarly spreading and monopolizing neglected gardens and waste ground, Mass. and N.Y. to Md."


HABITATS IN NEW ENGLAND

Edge, Floodplain Forest, Open Disturbed Area, Railroad Right-of-Way, River or Stream, Roadside, Utility Right-of-Way, Vacant Lot, Wet Meadow

Polygonum sachalinense is found at sites with varying combinations of sun, moist soil and human disturbance, such as stream banks, wet meadows, waste places and roadsides.


THREATS

Polygonum sachalinense is capable of quickly forming dense stands where it can crowd out native vegetation. Once established, these stands are very difficult to eradicate.


MANAGEMENT LINKS

Washington State Noxious Weed Control Board
Comprehensive information


DOCUMENTATION NEEDS

Documentation required: Herbarium specimen or mounted snippet of the branch with flowers or fruits.
Best time for documentation: Summer, fall.


ADDITIONAL INFORMATION

Washington State Noxious Weed Control Board
Comprehensive information

Wisconsin State Herbarium
Images, map, and general information

The Plants database
General information and map

Integrated Taxonomic Information System
Taxonomic information


REFERENCES

Bailey, J.P. 1990. Breeding Behaviour and Seed production in Alien Giant Knotweed in the British Isles. In: The biology and control of invasive plants. Conference organized by the Industrial Ecology group of the British Ecological Society at the University of Wales College of Cardiff.

Bailey, L.H.  1949.  Manual of Cultivated Plants.  Macmillan, New York.

Britton, N.L. and A. Brown.  1970.  An Illustrated Flora of the Northeastern United States vol. 2.  Dover Publications Inc., New York. 

Carter, M.F. and J.B. Grace. 1990. Relationships between flooding tolerance, life history, and short-term competitive performance in three species of Polygonum. Am. J. of Bot. 77:381-387.

Fernald, M.L. 1950. Gray's Manual of Botany, 8th ed. American Book Co., Boston. 

Gleason, H.A. and A.C. Cronquist.  1991.  Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed.  New York Botanical Garden, Bronx, New York.

Holmgren, N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual.  New York Botanical Garden, Bronx, New York.

Magee, D.W and H.E. Ahles. 1999.  Flora of the Northeast. University of Massachusetts Press, Amherst.

Patterson, D.T., D. Longstreth, M. Peet. 1977. Photosynthetic Adaptation to Light Intensity in Sakhalin Knotweed (Polygonum sachalinense). Weed Science 25(4): 319-323.

Seiger, L. 1995. Polygonum cuspidatum. The Nature Conservancy Element Stewardship Abstract.

Seymour, F.C. 1969. The Flora of New England. Charles E. Tuttle Company, Inc., Tokyo, Japan.

USDA, NRCS.  2001.  The PLANTS Database, Version 3.1. (http://plants.usda.gov)  National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Zika, P.F. and A.L. Jacobson.  2003.  An overlooked hybrid Japanese knotweed (Polygonum cuspidatum x sachalinense; Polygonaceae) in North America.  Rhodora 105(922): 143-152.