Common names: Himalayan knotweed
Persicaria wallichii (Himalayan knotweed) is a perennial herb/ (family Polygonaceae) with white flowers and narrow leaves found in the north and central coast ranges of California. It is native to south-central Asia. It favors grasslands, wetlands, bog and marsh, and riparian and bottomland habitat. It spreads via small fragments that form new plants. Means of dispersal include wind, water, animals and humans.
Cal-IPC Rating: Watch
CDFA Rating: -*?
Plant Risk Assessment
Plant Risk Assessment- An evaluation of the potential for a plant to be invasive in California.
Species ID Card
Invasive Species ID Card - To support field identification of early detection species, Cal-IPC has designed a set of Species ID cards that can be downloaded, printed double-sided, and trimmed to size.
Weed Management NotesNo Weed RIC Management Notes are available for this species. Check for information on other species in the genus on the Weed RIC site.
Cal-IPC Newsletter Articles
- Snapshots from the field. Lindgren, Jackie; Eberwein, Amy; Parish, Julie; Chapple, Tanya. Vol 26, Issue 1
- Eradicating knotweeds and other new invaders on California’s North Coast. Eberwein, Amy. Vol 24, Issue 3
- Japanese knotweed (Polygonum cuspidatum) and other knotweeds. Brusati, Elizabeth. Vol 13, Issue 1
Cal-IPC Symposium Presentations
Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.
- North coast invasive weeds – early detection rapid response eradication project. Reynolds, Candace (2023)
- North Coast invasive weeds: Early detection rapid response eradication project. Ferson, Susannah; Avila-Martinez, Carla (2021)
Other Persicaria wallichii Information
- CalPhotos - Images of plants taken mostly in California.
- Calflora - Distribution map and records of this species in California.
- EDDMapS - Distribution of this species in North America.
- Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
- USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.