Mid-Atlantic Invaders Tool

Japanese knotweed

Reynoutria japonica

Sieb. & Zucc.

Taxon, Habit: Plant, Forb

Habitat: Terrestrial/Wetland

U.S. Nativity: Introduced

Species Synonym(s): None

Common Name(s): None

Family: Polygonaceae (Buckwheat Family)

Family Synonym(s): None

Native Range (GRIN):

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Plant

Leslie J. Mehrhoff, University of Connecticut

Flower

Leslie J. Mehrhoff, University of Connecticut

Fruit

Jan Samanek, Phytosanitary Administration

Twig/Shoot

Leslie J. Mehrhoff, University of Connecticut

Flower

Bradley Kriekhaus, USDA Forest Service

Foliage

Jack Ranney, University of Tennessee

Foliage

Ohio State Weed Lab , The Ohio State University

Plant

Jan Samanek, Phytosanitary Administration

Description

Japanese knotweed is a dense growing shrub reaching heights of 10 ft. (3 m). The semi-woody stem is hollow with enlarged nodes. Leaves are alternate, 6 in. (15.2 cm) long, 3-4 in. (7.6-10 cm) wide and broadly-ovate. Flowering occurs in late summer, when small, greenish-white flowers develop in long panicles in the axils of the leaves. Plants are dioecious (male and female flowers occur on separate plants). Japanese knotweed commonly invades disturbed areas with high light, such as roadsides and stream banks. Reproduction occurs both vegetatively (rhizomes) and seeds, making this plant extremely hard to eradicate. The dense patches shade and displace other plant life and reduce wildlife habitat. Japanese knotweed resembles giant knotweed (Polygonum sachalinense), but giant knotweed is larger and has heart-shaped leaves. Japanese knotweed is native to eastern Asia and was first introduced into North America in the late 1800s.

Uses

Landscape Ornamental Use (GRIN): Yes

All Uses (GRIN): Ornamental, Vegetable, Fodder, Potential seed contaminant

Distribution Map (EDDMapS)

Wetland Indicator

Summary: Japanese knotweed (Reynoutria japonica) is a Terrestrial/Wetland species.

Atlantic and Gulf Coastal Plain (AGCP):

Mid-Atlantic Coastal Plain regions

Eastern Mountains and Piedmont (EMP):

Mid-Atlantic Piedmont and Mountain regions

Northcentral and Northeast (NCNE):

Northern parts of PA and NJ (and beyond)


Legend (data from U.S. Army Corps of Engineers)

OBL (Obligate wetland): Almost always occurs in wetlands (estimated probability > 99%) under natural conditions

FACW (Facultative wetland): Usually occurs in wetlands (estimated probability 67% - 99%), but occasionally found in non-wetlands

FAC (Facultative): Equally likely to occur in wetlands (estimated probability 34% - 66%) or non-wetlands

FACU (Facultative upland): Usually occur in non-wetlands (estimated probability 67% - 99%), but occasionally found in wetlands (estimated probability 1% - 33%)

UPL (Obligate upland): Occur almost always (estimated probability > 99%) in non-wetlands under natural conditions

Taxonomic Rank

Kingdom: Plantae
Phylum: Magnoliophyta
Class: Magnoliopsida
Subclass: Caryophyllidae
Order: Polygonales
Family: Polygonaceae
Genus: Reynoutria
Subject: Reynoutria japonica Sieb. & Zucc.

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