Fallopia sachalinensis

Giant knotweed

Family: Polygonaceae · Type: perennial · Not Native

Conservation status: Cal-IPC Yes

Giant knotweed is a naturalized perennial found in coastal California regions including northern Coast, San Francisco Bay, and southern Coast areas in disturbed places at elevations below 500 meters. Flowering from August to September, this plant produces small green-white flowers in compact panicle-like clusters 3 to 8 centimeters long. Growing in dense clumps with robust erect stems 2 to 4 meters tall, it spreads through extensive rhizomatous root systems. Its large ovate-oblong leaves measure 15 to 30 centimeters long, with heart-shaped bases and pointed tips, and feature distinctive minute dots on the leaf undersides. The smooth, shiny brown fruits are small, measuring 2.8 to 4.5 millimeters long and enclosed within the plant's perianth.

Habitat: Disturbed places

Bloom period: Aug-Sep

Elevation: < 500 m

Bioregions: NCo, SnFrB, SCo, expected elsewhere

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