Plant Image
Flower spike

Yavapai County Native & Naturalized Plants

Polygonum amphibium - water knotweed

Other Common Names: water smartweed
Plant Form: Forb

Family: Polygonaceae

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Forb Plant Description

Origin: Native   Life Cycle: Perennial
General Desc: Freely rooting from rhizomes, long, prostrate stems growing across mud or in water and topped with erect, dense, narrowly egg-shaped, pink flower clusters.
Identification notes: Rhizomatous perennial, aquatic or amphibious or terrestrial. Stems not twining. Leaves basal and alike, elliptic or rounded, not jointed with the stipule sheath. Spike-like flower heads of pink flowers are short and thick, terminal or nearly so.
Height: Stems 3 to 6 feet


Habitat Description: Marshes, ponds and lakes.
Plant Communities: Riparian
Elevation: 5000 - 9000 feet

Flower Characteristics

Color: Deep pink     Shape: Regular in elongated clusters     Tubular: Y     Flowering Period: Jun - Sep
Description: Individual flowers are tiny, less than 1/4 inch wide and 3/16 inch long, and form a slender, 2 inch long, terminal cluster. Tepals (sepals and petals) 5, bluntly rounded above, united below.

Leaf and Stem Characteristics

Leaf Color: Dark green     Leaf Type: Simple     Leaf Shape: Round or oval     Leaf Margin: Smooth     Leaf Attachment: Alternate     Leaves Clasp: N
Hairs: No     Spines: N
Leaf Description: Leaves are shiny and leathery; mainly floating; 6 inches long.

Fruit and Seed Characteristics

No Fruit or seed notes

  Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr #C
Prescott, AZ 86305
(928) 445-6590
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Last Updated: May 10, 2017  
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