''Persicaria hydropiper'' ( syn. ''Polygonum hydropiper''), also known as water pepper, marshpepper knotweed, arse smart or tade, is a plant of the family

Polygonaceae The Polygonaceae are a Family (biology), family of flowering plants known Common name, informally as the knotweed family or smartweed—buckwheat family in the United States. The Botanical name, name is Basionym, based on the genus ''Polygonum'', ...

. A widespread species, ''Persicaria hydropiper'' is found in Australia, New Zealand, temperate Asia, Europe and North America. The plant grows in damp places and shallow water. Cultivated varieties are eaten in

East Asia East Asia is a geocultural region of Asia. It includes China, Japan, Mongolia, North Korea, South Korea, and Taiwan, plus two special administrative regions of China, Hong Kong and Macau. The economies of Economy of China, China, Economy of Ja ...

for their pungent flavor.

Description

Water pepper is an annual herb with an erect stem growing to a height of . The leaves are alternate and almost stalkless. The leaf blades are narrowly ovate and have entire margins fringed by very short hairs. They are tapering with a blunt apex. Each leaf base has stipules which are fused into a stem-enclosing sheath that is loose and fringed at the upper end. 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 nodding spike. The perianth of each tiny flower consists of four or five segments, united near its green base and white or pink at the edges. There are six stamens, three fused carpels and three styles. The fruit is a dark brown oval, flattened nut. ''P. hydropiper'' is an

annual Annual may refer to: *Annual publication, periodical publications appearing regularly once per year **Yearbook **Literary annual *Annual plant *Annual report *Annual giving *Annual, Morocco, a settlement in northeastern Morocco *Annuals (band), a ...

, and prefers damp environments for optimal growth; it will readily grow in

riparian zone A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripari ...

s on the banks of streams and rivers, but can also grow in other areas where water collects, such as on the banks of

canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface ...

s, tyre and hoof tracks in woodlands, waterlogged soil, and around gates in fields. ''P. hydropiper'' is also tolerant of partial shade and base-poor soil. In the United Kingdom, where the plant is native, it can grow at any altitude between sea level and 505 metres.

Biochemistry

Water pepper has several

active ingredient An active ingredient is any ingredient that provides biologically active or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure or any function of the body of humans or animals. ...

s. Two bicyclic

sesquiterpenoid Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many combinations. Biochemical modifications such ...

s are present,

polygodial Polygodial is chemical compound found in dorrigo pepper, mountain pepper, horopito, canelo, paracress, water-pepper, and '' Dendrodoris limbata''. Chemically it is a drimane-type sesquiterpene dialdehyde of formula C15H22O2. Polygodial ...

(tadeonal, an unsaturated

dialdehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

with a drimane backbone), and warburganal, which gives it its pungent taste. The plant also contains

rutin Rutin (rutoside, quercetin-3-O-rutinoside or sophorin) is the glycoside combining the flavonol quercetin and the disaccharide rutinose (α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranose). It is a flavonoid glycoside found in a wide variety of pla ...

, a source of the bitter taste impression. Water pepper contains an

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...

(0.5%) which consists of

monoterpenoid Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear (acyclic) or contain rings (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen funct ...

s and

s: α-pinene, β-pinene, 1,4-cineol,

fenchone Fenchone is an organic compound classified as a monoterpenoid and a ketone. It is a colorless oily liquid. It has a structure and an odor similar to those of camphor. Fenchone is a constituent of absinthe and the essential oil of fennel. Fench ...

α-humulene Humulene, also known as α-humulene or α-caryophyllene, is a naturally occurring monocyclic sesquiterpene (C15H24), containing an 11-membered ring and consisting of 3 isoprene units containing three nonconjugated C=C double bonds, two of them b ...

β-caryophyllene Caryophyllene (), more formally (−)-β-caryophyllene (BCP), is a natural bicyclic sesquiterpene that occurs widely in nature. Caryophyllene is notable for having a cyclobutane ring, as well as a ''trans''-double bond in a 9-membered ring, both ...

trans-β-bergamotene Bergamotenes are a group of isomeric chemical compounds with the molecular formula C15H24. The bergamotenes are found in a variety of plants, particularly in their essential oils. There are two structural isomers, α-bergamotene and β-bergamot ...

Carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

s ( cinnamic,

valeric Valeric acid or pentanoic acid is a straight-chain alkyl carboxylic acid with the chemical formula . Like other low-molecular-weight carboxylic acids, it has an unpleasant odor. It is found in the perennial flowering plant ''Valeriana officina ...

and

caproic acid Caproic acid, also known as hexanoic acid, is the carboxylic acid derived from hexane with the chemical formula . It is a colorless oily liquid with a fatty, cheesy, waxy odor resembling that of goats or other barnyard animals. It is a fatty acid ...

) and their

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s were present in traces. The composition depends strongly on genetic factors. Wild water pepper produces oils that cause skin irritation.

Uses

Water pepper is eaten in

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

, where it is known as ''tade'' (蓼), or more specifically, ''yanagi tade'' (柳蓼). The

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

of cultivated plants are used as a

vegetable Vegetables are edible parts of plants that are consumed by humans or other animals as food. This original meaning is still commonly used, and is applied to plants collectively to refer to all edible plant matter, including edible flower, flo ...

, as the

wild type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, " ...

has a far more

pungent Pungency ( ) is the taste of food commonly referred to as spiciness, hotness or heat, found in foods such as chili peppers. Highly pungent tastes may be experienced as unpleasant. The term piquancy ( ) is sometimes applied to foods with a lower ...

taste. The herb is usually sold in markets as seedlings. Young red sprouts are known as ''beni-tade'' (紅蓼), and are used to garnish

sashimi is a Japanese cuisine, Japanese delicacy consisting of fresh raw fish or Raw meat, meat sliced into thin pieces and often eaten with soy sauce. Origin The word ''sashimi'' means 'pierced body', i.e., "wikt:刺身, 刺身" = ''sashimi'', whe ...

tempura is a typical Japanese dish that usually consists of seafood and vegetables that have been coated in a thin batter and deep-fried. Tempura originated in the 16th century, when Portuguese Jesuits brought the Western-style cooking method of ...

, and

sushi is a traditional Japanese dish made with , typically seasoned with sugar and salt, and combined with a variety of , such as seafood, vegetables, or meat: raw seafood is the most common, although some may be cooked. While sushi comes in n ...

. It is popular for summer cooking. The seeds may also be added to

wasabi Wasabi (Japanese language, Japanese: , , or , ) or Japanese horseradish (''Eutrema japonicum'' syn. ''Wasabia japonica'') is a plant of the family Brassicaceae, which also includes horseradish and Mustard plant, mustard in other genus, genera. ...

. Water pepper sauce, known as ''tade-zu'' (蓼酢), is a sauce traditionally made from finely chopped water pepper leaves, soaked in

vinegar Vinegar () is an aqueous solution of diluted acetic acid and trace compounds that may include flavorings. Vinegar typically contains from 5% to 18% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting ...

, and a small amount of

steamed rice Cooked rice refers to rice that has been cooked either by steaming or boiling. The terms steamed rice or boiled rice are also commonly used. Any variant of Asian rice (both indica and japonica varieties), African rice or wild rice, glutino ...

. Occasionally, the juice from a squeezed

kabosu Kabosu (カボス or 臭橙; binomial name: ''Citrus sphaerocarpa'') is a citrus fruit of an evergreen broad-leaf tree in the family Rutaceae. It is popular in Japan, especially Ōita Prefecture, where its juice is used to improve the taste of ...

is added. In

Japanese cuisine Japanese cuisine encompasses the regional and traditional foods of Japan, which have developed through centuries of political, economic, and social changes. The traditional cuisine of Japan (Japanese language, Japanese: ) is based on rice with m ...

it is traditionally used as a complement to

grilled Grilling is a form of cooking that involves heat applied to the surface of food, commonly from above, below or from the side. Grilling usually involves a significant amount of direct, radiant heat, and tends to be used for cooking meat and v ...

freshwater fish Freshwater fish are fish species that spend some or all of their lives in bodies of fresh water such as rivers, lakes, ponds and inland wetlands, where the salinity is less than 1.05%. These environments differ from marine habitats in many wa ...

, but not saltwater fish. In China, water pepper is known as ''la liao'' (辣蓼), and used in

traditional Chinese medicine Traditional Chinese medicine (TCM) is an alternative medicine, alternative medical practice drawn from traditional medicine in China. A large share of its claims are pseudoscientific, with the majority of treatments having no robust evidence ...

. In Indian traditional medicine, leaves of ''P. hydropiper'' are used against intestinal helminth infections. A study has proved that ''P. hydropiper'' leaves possess noteworthy anthelmintic efficacy and justify their use in traditional medicine against intestinal worms. DOI: 10.1007/s12639-022-01559-2 In Europe, water pepper was once cultivated and eaten during war time as a substitute for pepper. The plant contains many acids, including

formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid. It has the chemical formula HCOOH and structure . This acid is an important intermediate in chemical synthesis and occurs naturally, most notably in some an ...

, which makes it unpalatable to livestock.Illinois Wildflowers
/ref> Though mammals do not eat wild water pepper, some insects do, giving rise to the Japanese saying "''Tade kuu mushi mo sukizuki''" (蓼食う虫も好き好き "Some insects eat water pepper and like it"), which may be translated as "There is no accounting for taste" or "Each to his own."

Gallery

Polygonum hydropiper1.jpg Persicaria hydropiper.JPG Polygonum hydropiper3.jpg Polygonum hydropiper2.jpg Polygonum hydropiper — Flora Batava — Volume v6.jpg, Illustration from Jan Kops' ''Flora Batava'' (1832) Polygonum hydropiper (1832).jpg, Illustration from ''La flore et la pomone françaises'' (1832) 356 Polygonum tomentosum, Polygonum hydropiper.jpg, Illustration from ''Bilder ur Nordens Flora'' (1917–1926)

References

External links