''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 North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, and parts of

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

, 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 A noxious weed, harmful weed or injurious weed is a weed that has been designated by an agricultural or other governing authority as a plant that is harmful to agricultural or horticultural crops, natural habitats or ecosystems, or humans or lives ...

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 In ecology, a marsh is a wetland that is dominated by herbaceous plants rather than by woody plants.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p More in genera ...

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 hori ...

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 Aquatic plants, also referred to as hydrophytes, are vascular plants and Non-vascular plant, non-vascular plants that have adapted to live in aquatic ecosystem, aquatic environments (marine ecosystem, saltwater or freshwater ecosystem, freshwater ...

, 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 In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...

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 An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple fruit, simple dry fruits, dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and Dehi ...

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

, ''P. a.'' var. ''stipulacea'' does not grow south of the Laurentide Ice Sheet 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 ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods, but excluding the amniotes (tetrapods with an amniotic ...

Flora of Northern 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 Freshwater plants