''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 Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

, and parts of

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, and it grows elsewhere as an

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived ther ...

and sometimes a noxious weed.

Distribution and habitat

''Persicaria amphibia'' is native to a large area across the northern hemisphere, including Europe, Asia, North America, and parts of Africa. It has been introduced elsewhere, such as South America and other parts of Africa. It grows in many types of wet habitat, such as ponds, streams, and

marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...

es. It is a

rhizomatous In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow ho ...

perennial herb which takes a variety of forms and is quite variable in

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

. It may be an aquatic plant, growing submerged or floating in water bodies, it may grow in muddy and wet areas which are periodically inundated, and it may grow in moist spots on land, such as in meadows. Dry-land and fully aquatic plants are sometimes considered different named varieties of the species.

Description

''Persicaria amphibia'' produces a thick stem from its rhizome. The stem may creep, float, or grow erect, rooting at stem nodes that come in contact with moist substrate. Stems are known to reach 3 meters (10 feet) long in aquatic individuals. The stems are ribbed and may be hairless to quite hairy in texture. Leaves are lance-shaped or take various other shapes and are borne on petioles. They may be over 30 centimeters (1 foot) in length. The

inflorescence An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...

is a dense terminal cluster of many five-lobed pink flowers. Plants may have bisexual or unisexual flowers, with some plants bearing only male or only female flowers. The fruit is a shiny brown rounded achene around long.

Varieties

Three varieties are generally recognized, though some authorities consider ''P. a.'' var. ''emersa'' a distinct species, ''Persicaria coccinea''. * ''P. a.'' var. ''emersa'' (longroot smartweed) – Plants palustrine, usually with emergent leafy stems; ocreae never with flared apices; aerial leaves petiolate with acuminate tips; inflorescence spikes terminal, usually 2 (unequal), > 4 cm long. *''P. a.'' var. ''stipulacea'' – Plants aquatic, usually with floating stems and leaves; ocreae with flared apices (when stranded); aerial leaves (when present) nearly sessile with somewhat cordate bases and blunt apices; inflorescence spikes usually 1, greater than long. In North America, ''P. a.'' var. ''stipulacea'' does not grow south of the

Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million year ...

except in the mountain west and Mexico. *''P. a.'' var. ''amphibia'' – European Persicaria amphibia-emersa.jpg, ''P. a.'' var. ''emersa'' long spike Persicaria amphibia-emersa short.jpg, ''P. a.'' var. ''emersa'' short spike Persicaria amphibia stipulacea.jpg, ''P. a.'' var. ''stipulacea'' aquatic form Persicaria amphibia-stipulacea terrestrial.jpg, ''P. a.'' var. ''stipulacea'' terrestrial form Persicaria_amphibia_sl1.jpg, ''P. a.'' var. ''amphibia''

Uses

Various parts of this plant were used by several Native American groups as medicinal remedies and sometimes as food.''Polygonum amphibium''.
Native American Ethnobotany. University of Michigan, Dearborn.

References

{{Taxonbar, from=Q157569

amphibia Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbor ...

Flora of North America Flora of Europe Flora of Asia Plants described in 1753 Taxa named by Carl Linnaeus Plants used in Native American cuisine Plants used in traditional Native American medicine