Persicaria wallichii
Himalayan knotweed
(c) Dee Shea Himes, some rights reserved (CC BY), uploaded by Dee Shea Himes · licence
Family: Polygonaceae · Type: Herb · Not Native
Conservation status: Cal-IPC Yes
Persicaria wallichii (Himalayan knotweed) is a non-native California herb in the Polygonaceae family, recognized by broad cordate leaves and panicle-like inflorescence distinctive.
Himalayan knotweed is a naturalized perennial herb found in northern California Coast and northern central Coast counties, particularly in Del Norte and Humboldt counties, in moist disturbed places and marshes at elevations below 500 meters. Flowering from August to October, this plant produces white to pink flowers in panicle-like clusters 40 to 120 millimeters long with distinctive red to purple anthers. Growing with ascending or erect stems 7 to 12 centimeters tall (occasionally to 250 centimeters), it develops adventitious roots and has a woody or non-woody base. Its large leaves measure 9 to 22 centimeters long, with cordate to truncate bases and acuminate tips, and are slightly hairy on the underside with glabrous or hairy upper surfaces. The fruit is a small, 3-angled brown achene measuring 2.1 to 2.5 millimeters long, often with a minutely rough texture.
Identification and appearance
Key characters: 6 sympatric species; broad cordate leaves and panicle-like inflorescence distinctive
Habitat and range
Habitat: Moist disturbed places, marshes
Elevation: < 500 m
Outside California: Oregon, British Columbia, native to south-central Asia
Bloom period
Persicaria wallichii blooms Aug-Oct.
Conservation status
Cal-IPC Yes
How to tell it apart
vs Polygonum: Persicaria has opaque stem sheaths; Polygonum has translucent sheaths that split into two lobes.; vs Rumex: Persicaria has spike-like pink/white flower clusters; Rumex has branched greenish flower clusters.; vs Trifolium: Persicaria has spike/head flower clusters and papery stem sheaths; Trifolium has clover heads and no sheaths.; vs Salix: Persicaria is an herb with flower spikes; Salix is a woody shrub with catkins.; vs Phytolacca: Persicaria has small pink/white flowers in spikes; Phytolacca has white-green flowers and dark purple berries.
Frequently asked questions
Is Persicaria wallichii native to California?
No. Persicaria wallichii is not native to California (recorded as not native).
When does Persicaria wallichii bloom?
Persicaria wallichii blooms Aug-Oct.
What plant family does Persicaria wallichii belong to?
Persicaria wallichii is in the Polygonaceae family, genus Persicaria.
Is Persicaria wallichii invasive in California?
Persicaria wallichii is listed by Cal-IPC with an invasiveness rating of Yes.
What habitat does Persicaria wallichii grow in?
Persicaria wallichii grows in Moist disturbed places, marshes.
Related species
Other California species in the same genus, family, or bioregion.
- Persicaria amphibia — Water smartweed
- Persicaria capitata — Himalayan smartweed
- Persicaria hydropiper — Waterpepper
- Persicaria hydropiperoides — False waterpepper
- Persicaria lapathifolia — Willow weed
- Persicaria maculosa — Lady's thumb
- Polygonaceae sp. — Buckwheat family
- Polygonum argyrocoleon — Persian knotweed
- Polygonum austiniae — Mrs. austin's knotweed
- Polygonum aviculare — Knotweed
Sources: Jepson eFlora · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.