Fallopia sachalinensis
Giant knotweed
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Family: Polygonaceae · Type: Perennial · Not Native
Conservation status: Cal-IPC Yes
Fallopia sachalinensis (Giant knotweed) is a non-native California perennial in the Polygonaceae family, recognized by largest species with cordate leaf bases and many-celled hairs on veins.
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.
Identification and appearance
Key characters: 3 sympatric species; largest species with cordate leaf bases and many-celled hairs on veins
Habitat and range
Habitat: Disturbed places
Elevation: < 500 m
Outside California: native to central Asia
Bloom period
Fallopia sachalinensis blooms Aug-Sep.
Conservation status
Cal-IPC Yes
How to tell it apart
vs Sonchus: Fallopia has smooth-edged leaves; Sonchus has deeply lobed leaves with prickly edges and milky sap.; vs Oxyria: Fallopia is a climbing vine; Oxyria is an upright herb with kidney-shaped basal leaves.; vs Bistorta: Fallopia climbs with heart-shaped leaves; Bistorta grows upright with dense flower spikes.; vs Persicaria: Fallopia is a climbing vine; Persicaria is upright or sprawling, not climbing.; vs Aconogonon: Fallopia climbs; Aconogonon forms upright clumps in high mountains.
Frequently asked questions
Is Fallopia sachalinensis native to California?
No. Fallopia sachalinensis is not native to California (recorded as not native).
When does Fallopia sachalinensis bloom?
Fallopia sachalinensis blooms Aug-Sep.
What plant family does Fallopia sachalinensis belong to?
Fallopia sachalinensis is in the Polygonaceae family, genus Fallopia.
Is Fallopia sachalinensis invasive in California?
Fallopia sachalinensis is listed by Cal-IPC with an invasiveness rating of Yes.
What habitat does Fallopia sachalinensis grow in?
Fallopia sachalinensis grows in Disturbed places.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · CalPhotos
Last updated 2026-10-01
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.