Calflora, a 501c3 non-profit
Distribution by County   6735    
Polygonum amphibium  L.  var. emersum  Michx.

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

Alameda: 11 Los Angeles: 11 Plumas: 19 Santa Cruz: 31
Alpine: 3 Marin: 23 Riverside: 3 Shasta: 7
Butte: 15 Mariposa: 1 Sacramento: 10 Sierra: 2
Colusa: 5 Mendocino: 10 San Benito: 1 Siskiyou: 4
Contra Costa: 11 Merced: 7 San Bernardino: 29 Solano: 7
El Dorado: 17 Modoc: 1 San Diego: 49 Sonoma: 9
Fresno: 2 Mono: 12 San Francisco: 14 Stanislaus: 3
Glenn: 9 Monterey: 25 San Joaquin: 5 Sutter: 5
Inyo: 5 Napa: 3 San Luis Obispo: 42 Tehama: 3
Kern: 3 Nevada: 4 San Mateo: 44 Tuolumne: 2
Lake: 13 Orange: 14 Santa Barbara: 37 Ventura: 15
Lassen: 19 Placer: 4 Santa Clara: 29 Yolo: 4

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: 11/21/2024).