Water Knotweed

(Persicaria amphibia)

Water Knotweed (Persicaria amphibia)

Samuel A. Schmid

CC BY 4.0

Image By: Samuel A. Schmid

Recorded By:

Estimated Native Range

Summary

Persicaria amphibia, commonly known as Water Knotweed, is a deciduous perennial herb that thrives in a variety of wetland habitats including marshes, shores, and riparian zones across the Northern Hemisphere. It exhibits a remarkable ability to adapt to its environment, with stems that may creep, float, or grow erect, often rooting at nodes when in contact with moist substrates. Aquatic forms can have stems reaching up to 3 meters (10 feet) in length. The plant is characterized by its dense terminal clusters of many five-lobed pink flowers, which bloom from mid-summer to early fall, adding a splash of color to its surroundings. The flowers can be bisexual or unisexual, with some plants exclusively bearing male or female flowers. The fruit is a shiny brown, rounded achene approximately 3 mm (0.12 in) long.

Water Knotweed is valued for its ability to stabilize soil and provide habitat for wildlife, making it useful for riparian restoration projects. It is also used ornamentally in water gardens and naturalized pond edges. In cultivation, it requires full sun to part shade, high amounts of water, and soils with slow drainage to mimic its natural wetland conditions. However, gardeners should be cautious as Persicaria amphibia can be invasive outside its native range, potentially outcompeting native vegetation.CC BY-SA 4.0

Plant Description

Plant Type: Herb
Height: 0.3-0.5 feet
Width: 0.2-0.4 feet
Growth Rate: Moderate
Flower Color: Pink
Flowering Season: Spring, Summer
Leaf Retention: Deciduous

Growth Requirements

Sun: Full Sun, Part Shade
Water: High
Drainage: Slow, Standing

Common Uses

Bank Stabilization, Bee Garden, Bird Garden, Butterfly Garden, Low Maintenance, Rabbit Resistant, Salt Tolerant, Showy Flowers, Water Garden

Natural Habitat

Thrives in marshes, shores, and riparian zones across the Northern Hemisphere

Other Names

Common Names: Longroot Smartweed , Water Smartweed , Amphibious Bistort , Vand-Pileurt , Wasserknöterich , Vesitatar , Persicaire Amphibie , Vasslirekne , Veenwortel , Vattenpilört

Scientific Names: Polygonum amphibium , Persicaria amphibia , Polygonum aquaticum , Polygonum natans , Polygonum amphibium var. terrestre , Persicaria amphibia var. terrestre , Polygonum amphibium var. aquaticum , Polygonum muhlenbergii , Polygonum setiferum , Polygonum amphibium var. natans

GBIF Accepted Name: Persicaria amphibia (L.) Gray