两栖蓼（学名：Polygonum amphibium）为蓼科蓼属下的一个种。

Persicaria amphibia (syn. Polygonum amphibium) is a species of flowering plant in the knotweed family known by several common names, including longroot smartweed, water knotweed, water smartweed, and amphibious bistort. It is native to much of North America, Asia, Europe, and parts of Africa, and it is known elsewhere as an introduced species and sometimes a noxious weed.