Persicaria amphibia, commonly known as Water Smartweed or Longroot Smartweed, is a rhizomatous perennial herb that thrives in a variety of wetland habitats, including the margins of ponds and lakes, slow-moving streams, marshes, and wet meadows. It is native to a broad region encompassing much of North America, Asia, Europe, and parts of Africa. The plant exhibits remarkable plasticity, occurring as both aquatic and terrestrial forms, depending on the water level. It typically has stems that can reach up to 10 feet in length and lance-shaped leaves that may grow up to 1 foot long. The flowers are small, pink, and arranged in dense, spike-like inflorescences that bloom from mid-summer to early fall.

Water Smartweed is valued for its ability to stabilize soil and provide habitat for wildlife in wetland areas. It is also used for ornamental purposes in water gardens and naturalized pond settings. In cultivation, it prefers full sun to part shade and requires consistently moist or even saturated soil conditions. While it can be a vigorous grower, it is generally not problematic in its native range. However, Persicaria amphibia var. emersa is known to be potentially invasive in some regions outside its native habitat. Gardeners should be cautious and consult local regulations before planting it in non-native areas. Its invasive potential is due to its aggressive growth and ability to form dense mats that can outcompete native vegetation.CC BY-SA 4.0