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Swamp Knotweed
Persicaria amphibia
About Swamp Knotweed (Persicaria amphibia) Nurseries Show All Photos Swamp Knotweed (Polygonum amphibium) is a common native perennial herb in the Polygonaceae (Buckwheat) family that grows throughout California in almost every county. It is a wetland plant that is moderately fast growing and moderately long-lived. It grows in a rounded form to a height of 0.1 foot, with active growth during the summer. Flowers are yellow and bloom in the late spring. Leaves are medium green and deciduous. It tends to grow in shallow lakes and streams, at elevations from 0-10000 feet.
Plant Description
Plant Type
Perennial herb

Max. Height
7.9 - 1.2 in (20.1 - 3 cm)

Winter Deciduous

Flower Color

Native Status

Natural Setting
Site Type
Shallow lakes, streams, shores

Part Shade

Elevation ?
-17' - 9352'

Annual Precip. ?
4.9" - 87.3"

Summer Precip. ?
0.15" - 3.52"

Coldest Month ?
26.3° F - 53.8° F

Hottest Month ?
50.6° F - 80.5° F

Humidity ?
0.14 vpd - 29.37 vpd

Sunset Zones ?
1*, 2*, 3*, 4*, 5*, 6*, 7*, 8*, 9*, 14*, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24

Landscaping Information
Common uses
Bogs and Ponds

Other Names
Botanical Names
Polygonum amphibium,Polygonum amphibium var. emersum

Common Names
Water Knotweed, Water Smartweed

Sources include: Wikipedia. All text shown in the "About" section of these pages is available under the Creative Commons Attribution-ShareAlike License. Plant observation data provided by the participants of the California Consortia of Herbaria, Sunset information provided by Jepson Flora Project. Propogation from seed information provided by the Santa Barbara Botanical Garden from "Seed Propagation of Native California Plants" by Dara E. Emery. Sources of plant photos include CalPhotos, Wikimedia Commons, and independent plant photographers who have agreed to share their images with Calscape. Other general sources of information include Calflora, CNPS Manual of Vegetation Online, Jepson Flora Project, Las Pilitas, Theodore Payne, Tree of Life, The Xerces Society, and information provided by CNPS volunteer editors, with special thanks to Don Rideout. Climate data used in creation of plant range maps is from PRISM Climate Group, Oregon State University, using 30 year (1981-2010) annual "normals" at an 800 meter spatial resolution.

Links:   Jepson eFlora Taxon Page  CalPhotos  Wikipedia  Calflora

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