Japanese Knotweed
Reynoutria japonica · Herbaceous Perennial (Shrub-like)
Plant Family
Polygonaceae
Tree Category
Invasive Perennial
Variety / Cultivar
None (Wild type)
Hardiness Zones
USDA Zones 4-9; highly resilient to extreme temperatures.
About This Tree
A fast-growing, bamboo-like herbaceous perennial that forms dense thickets. It has hollow stems and can reach heights resembling a small tree or large shrub.
Leaf Characteristics
Simple, broad-oval to heart-shaped (cordate), 3-6 inches long with a flat base and pointed tip, and alternate arrangement.
Bark Characteristics
Not true bark; stems are hollow, green with reddish-purple speckles, and segmented like bamboo.
Growing Information
Origin Region
East Asia (Japan, China, Korea); invasive globally
Growing Season
Rapid growth in spring/summer, flowers in late summer, dormant in winter
Sunlight & Water Needs
Full sun to partial shade; highly adaptable to various moisture levels including riparian zones.
Mature Size
7-15 feet in height; spreads indefinitely via underground rhizomes.
Special Characteristics
Extremely invasive, can grow through asphalt and concrete, highly resistant to many herbicides, and forms monocultures.
Wildlife & Ecology
Provides late-season nectar for bees and pollinators, but generally degrades local ecosystems by displacing native plants and reducing biodiversity.