Japanese knotweed, Mexican bamboo, Fleece flower
FULL SCIENTIFIC NAME
Polygonum cuspidatum Sieb. & Zucc.
FAMILY NAME COMMON
FAMILY SCIENTIFIC NAME
Synonyms: Fallopia japonica (Houtt.) Dcne., Pleuropterus cuspidatus (Sieb. & Zucc.) Moldenke, Pleuropterus zuccarinii (Small) Small, Polygonum zuccarinii Small, Reynoutria japonica Houtt.
Polygonum cuspidatum is an herbaceous perennial that appears woody, and reaches 1-3 m (3-10 ft.) in height. The round stems are hollow and covered with scales. The shoots grow from spreading rhizomes that can reach 20 m (65 ft.) in length. The leaves are broadly oblong-ovate or ovate-lanceolate, 8-15 cm (3-6 in.) long and 5-12 cm (2-4.75 in.) wide. The tips of the leaves are abruptly acuminate, while the bases of the leaves are truncate. The lower leaf surface lacks the minute trichomes that other similar species possess (see below). The numerous, greenish-white flowers of Polygonum cuspidatum are borne in panicles from the upper axils. These panicles measure 8-15 cm (3-6 in.) long. The flowers are functionally unisexual: each of the male and female flowers still have the complementary organs, but they are vestigial. The inflorescences of the male flowers tend to be upright, while those of the female flowers tend to be drooping. Flowers appear from August to September. The fruit are papery and winged, and are 6-10 mm (0.25-0.4 in.) long. These fruits contain black, smooth, shiny, 3-angled achenes that are 3-4 mm (0.2 in.) long. When frost hits this plant, it quickly turns brown and dies back for the year. Page References Bailey 348, Fernald 589, Gleason & Cronquist 139, Holmgren 124, Magee & Ahles 441, Newcomb 190. See reference section below for full citations.
Polygonum sachalinense F. Schmidt ex Maxim. (giant knotweed), Polygonum x bohemica (hybrid of P. cuspidatum and P. sachalinense) 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.
Though Polygonum cuspidatum produces winged fruits that can move some distance, it spreads mostly through long rhizomes. Rhizome fragments can sprout new plants, and the plant often disperses via natural or human-aided movement of such fragments.
Polygonum cuspidatum is native to China, Japan and Korea. In the United States it is found from Maine to Georgia and west from South Dakota to Oklahoma. In the western part of the country it is in Washington, Oregon, California, Idaho, Montana, Utah, Colorado and Alaska. This plant has been reported from all the states of New England.
HISTORY OF INTRODUCTION IN NEW ENGLAND
Polygonum cuspidatum was introduced from Japan to the United Kingdom probably sometime after 1830. It was first distributed around 1855 by the Royal Botanical Gardens at Kew. From here it was popularized through garden catalogs. By the early 1900's, the rampant nature of its growth was observed, and the plant began to decline in popularity. This plant was most likely brought into the United States from Britain close to the turn of the century for use as a horticultural plant. By 1894, it was reported as naturalized near Philadelphia, Pennsylvania, Schenectady, New York and Atlantic Highlands, New Jersey. Regardless of these early observations of naturalization, in 1910, it was being described in garden catalogs in this country. By 1938, information was already being published on how to get rid of the plant in gardens. As in other parts of the country, Polygonum cuspidatum was brought into New England for ornamental gardens. From the gardens it likely spread via rhizomes as well as some of the few viable seeds.
HABITATS IN NEW ENGLAND
Abandoned Field, Early Successional Forest, Edge, Floodplain Forest, Forest Wetland, Herbaceous Wetland, Open Disturbed Area, Roadside, Shrub Wetland, Vacant Lot, Wet Meadow, Yard or Garden. Polygonum cuspidatum can be found in a variety of habitats. It thrives in riparian areas and wetlands, but can be found along roadsides and other disturbed areas. It prefers full sunlight, but can tolerate moderate shade. This plant is tolerant of high temperatures, dry soil and salt. It is extremely intolerant of frost, and after the first frost, it turns brown and dies back for the season.
The threat of Polygonum cuspidatum was first recognized in Britain, where it has been present for a longer period of time. It appears to behave similarly here, forming dense, persistant thickets that exclude other vegetation. Its vegetative reproduction has proved quite successful. Established populations are difficult to eradicate.
Plant Conservation Alliance Fact sheet with control information
The Connecticut Invasive Plant Working Group Invasive Plant Management Guide
Documentation required: A photograph of the leaves. Best time for documentation: Summer, fall.
Adirondack Park Invasive Plant Program Identification, fact sheet, management and distribution information
Integrated Taxonomic Information System Taxonomic information
PLANTS Database General information and map
Plant Conservation Alliance Fact sheet including control information
Maine Natural Areas Program Fact sheet with descriptive information
Ohio Perennial and Biennial Weed Guide Photographs and description
Invasivespeciesinfo.gov Links to more information
Andersen, R.N. 1968. Germination and Establishment of Weeds for Experimental Purposes. Weed Science Society of America Handbook. WSSA, Illinois.
Bailey, L.H. 1949. Manual of Cultivated Plants. Macmillan, New York.
Fernald, M.L. 1950. Gray's Manual of Botany 8th ed. American Book Co., Boston.
Gleason, H.A. 1952. The New Britton and Brown Illustrated Flora of the Northeastern United States and Adjacent Canada. Macmillan Publishing Co., Inc. New York.
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.
Moul, E.T. 1948. A dangerous weedy Polygonum in Pennsylvania. Rhodora 50:64-66.
Newcomb N. 1977. Newcomb's Wildflower Guide. Little Brown, Boston.
Seiger, L.A. 1996. Fallopia japonica. p.77. In Randall, J.M. and J. Marinelli. [eds.]. Invasive Plants: Weeds of the Global Garden. Brooklyn Botanic Garden Inc., New York.
Sultan, S.E. 2001. Phenotypic plasticity for fitness components in Polygonum species of contrasting ecological breadth. Ecology 82 (2): 328-343.
Sultan, S.E., A.M. Wilczek, S.D. Hann, B.J. Brosi. 1998. Contrasting ecological breadth of co-occurring annual Polygonum species. Journal of Ecology 86 (3): 363-383.
Townsend, A. 1997. Japanese knotweed: a reputation lost. Arnoldia 57(3): 13-19.
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.