Amphibious Bistort – also called Water Smartweed, especially in North America – is a very versatile plant which adjusts its form to the prevailing water conditions and levels. Depending on the site, this species may be found either on land or as a floating plant in the Donau-Auen National Park.
Amphibious Bistort has a creeping rootstock with short stolons. The floating stem of the aquatic form of the species may reach a length of 3m; swimming leaves float on the surface. These are hairless and between 5 and 17cm long. On land, the plant may reach a height of 30cm to 1m. This form of the plant features leaves which have hairs, are narrower and have a more markedly pointed tip. On land, the species cannot be easily differentiated from other Bistort species. One clearly identifiable characteristic is however the base of the petiole, or leaf stalk. The leaf stalk of the Amphibious Bistort emerges from the upper half of the stipule leaf sheath. The reddish-pink flowers are arranged in compact terminal spikes.
The species' range includes the northern temperate zone as well as eastern India, South Africa and even Mexico. In Austria, Amphibious Bistort occurs sporadically in all provinces, wherever stagnant waters are to be found, in particular fish ponds and backwaters. The species may also be spotted in damp locations such as ditches or moist waste grounds, even up to montane levels.
Endangerment and Conservation Status
In the western Alps, this species is regionally vulnerable.
As a perennial, the Amphibious Bistort forms new growth each year by way of its rootstock, which is anchored in mud. By storing supporting tissue, the land form of Persicaria amphibia can grow an upwardly leaning stem. In contrast, when submerged the stem is diffused with air canals and large floating leaves with long stalks spread across the water's surface. If the water conditions should change, the plant can easily adapt to one or the other form. Flowering takes place from May to September. The fruit – a small nut – is rarely formed despite successful pollination. At higher elevations the short vegetation period is rarely sufficient for maturation of the fruit. In addition to stolons, Amphibious Bistort can also practice vegetative reproduction by way of shoots which easily build new roots.
The brownish-black, sharp-edged fruits are hydrophobic and can thus float for long periods of time.