Calflora, a 501c3 non-profit
Distribution by County   6734    
Polygonum amphibium  L.

(not an active name)
Swamp knotweed,   Water knotweed,   Water smartweed
Polygonum amphibium is a perennial herb that is native to California, and also found elsewhere in North America and beyond.
also called Persicaria amphibia
Record Count by County

Alameda: 8 Los Angeles: 8 Sacramento: 30 Sierra: 2
Alpine: 2 Marin: 20 San Benito: 1 Siskiyou: 2
Butte: 9 Mendocino: 12 San Bernardino: 34 Solano: 16
Colusa: 3 Merced: 4 San Diego: 46 Sonoma: 8
Contra Costa: 15 Modoc: 4 San Francisco: 6 Sutter: 1
El Dorado: 16 Mono: 12 San Joaquin: 3 Tehama: 4
Fresno: 3 Monterey: 22 San Luis Obispo: 36 Tuolumne: 4
Glenn: 6 Napa: 1 San Mateo: 39 Ventura: 13
Inyo: 3 Nevada: 5 Santa Barbara: 29 Yolo: 11
Kern: 2 Orange: 10 Santa Clara: 26
Lake: 11 Placer: 2 Santa Cruz: 28
Lassen: 15 Plumas: 15 Shasta: 3

Suggested Citation
Calflora: Information on California plants for education, research and conservation, with data contributed by public and private institutions and individuals, including the Consortium of California Herbaria. [web application]. 2024. Berkeley, California: The Calflora Database [a non-profit organization]. Available: https://www.calflora.org/   (Accessed: 12/03/2024).