Fallopia japonica

Japanese knotweed

Family: Polygonaceae · Type: perennial · Not Native

Conservation status: Cal-IPC Yes

Japanese knotweed is a naturalized perennial herb found in northern California's Central Coast and San Francisco Bay regions in disturbed places at elevations below 1,000 meters. Flowering from August to October, this invasive plant produces small white flowers in erect or spreading panicle-like clusters 3 to 10 centimeters long. Growing in dense clumps with erect stems 1 to 2 meters tall, it features a glaucous, glabrous stem with few branches. Its large widely ovate leaves measure 6 to 13 centimeters long, with truncate bases and acuminate tips, and feature one-celled hairs on the undersides of veins. The fruit is a dark brown, shiny achene 3.8 to 5 millimeters long, enclosed within the plant's white perianth.

Habitat: Disturbed places

Bloom period: Aug-Oct

Elevation: < 1000 m

Bioregions: n CA-FP (esp s NCoR), SnFrB

California counties: Shasta, Contra Costa, Siskiyou, Butte, Nevada, Humboldt, Santa Cruz

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Jepson eFlora, Cal-IPC, and more.