Persicaria hydropiper, syn. Polygonum hydropiper
- Marshpepper Knotweed
- Water Pepper
Water pepper is a plant belonging to the family Polygonaceae. This plant is found growing in damp locations and also in shallow water. Water pepper is found growing abundantly in various places including North America, temperate Asia, Europe, Australia and New Zealand. This herb has a pungent flavour and is mainly used in the form of a spice.
Water pepper is an annually growing herb with an erect stem that grows up to anything between 20 cm and 70 cm (8 inches to 28 inches) in height. Leaves of this herb are almost without stalk and arranged alternately. The leaf blades of water pepper have a barely ovate shape and with margins that are fringed with extremely short hair-like bristles.
The leaves of the water pepper plant are narrowing towards the apex, which is blunt. The base of each leaf comes with stipules that are joined together to form a sheath that encloses the plant’s stem. The fused stipules are loose as well as tasselled towards the upper end. The plant bears inflorescences resembling nodding spikes. The water pepper bears tiny flowers, whose perianth comprises anything between four and five segments that are joined close to the green base. The edges of the flowers have a white or pink hue. In all, each flower consists of six stamens of which three are fused carpels, while the remaining three are styles. Water pepper bears oval-shaped deep brown fruits resembling flattened nut.
The water pepper is a late bloomer as the flowers of this plant appear relatively later in the season. The last fruits of the plant fall on the snow and are dispersed by wind. An increase in the spread of the species is often attributed to changes in the waterside ecosystem induced by humans, for instance eutrophication. While this species is not found in most regions of Africa, it can safely be described as an almost cosmopolitan plant.
This species is an annually growing plant that has been employed in traditional herbal medicine as well as used for seasoning. The scientific name of this species – hydropiper – denotes water pepper. This is the reason why it is called water pepper in English. More so, because the leaves of this plant leave a burning pepper-like taste when consumed.
Since long, people have been using the water pepper (hydropiper) for treating a various ailments and health disorders. This herb is also used in the form of a spice in Japanese culinary. Usually, it is mixed with other spices and used in cooking. It is believed that drinking this spice soaked in wine helps to determine the sex of a still born child and help the expectant lady to give birth to a male child. Aside from its medicinal and culinary uses, water pepper has also been employed to impart yellow color to wool.
Water pepper possesses a number of therapeutic properties. This herb is antiseptic, diuretic, diaphoretic, emmenagogue and stimulant. An aqueous extract obtained from this herb is effective in treating amenorrhoea. Perhaps, an alcoholic extract of water pepper would be further effective in curing the condition. Using water pepper works to augment body heat with a type of formication that results in a bearing down sensation, making the pelvic region feel full. It has been found that using an infusion of the herb prepared with cold water helps to treat colds and cough, gravel and milk-sickness. When blended with wheat-bran, this infusion helps in treating bowel problems. Cholera patients in Asia have reported that they have been benefited by moistening a sheet with a hot decoction prepared from the plant and wrapping themselves with it. In some cases, patients are said to have completely recovered from cholera after using this remedy. It is said that when water pepper formulation is used together with gum myrrh and iron sulphate the blend has helped to cure epilepsy.
Water pepper is also used topically in the form of fomentation to treat gangrene. For this purpose, a formulation is prepared by boiling water pepper leaves in a mixture of water and vinegar. Aside from gangrene, people have also benefited by applying the infusion prepared with water pepper leaves to hemorrhoidal tumours and chronic ulcers. It is also effective when used as a wash in inflammations and chronic erysipelas as well as in the form of a fomentation in flatulent colic and tympanites. The fresh leaves bruised along with May-weed leaves and moistened with the oil of turpentine is applied topically to the skin to cure blisters.
It is said that the many empirics burn the dried water pepper plant and combine its ashes with the garden thyme (scientific name Thymus vulgaris) ashes and use the mixture to treat bladder stone and gravel. The mixture of the ashes of these two herbs is used in the form of an injection and also a solution and passed into the bladder to serve as a solvent for stone and gravel formed in the organ. However, this means of treatment is not only doubtful, but also hazardous.
An infusion of water pepper leaves prepared in cold water is said to be an external remedy for sore mouth, especially of nursing women as well as to treat mercurial ptyalism. This formulation is applied topically to the affected areas. However, the infusion or decoction prepared with the leaves of the plant in hot water has not been found as effective to those prepared in cold or tepid water.
People in Japan consume the leaves of water pepper as a leafy vegetable. However, they do not eat the leaves of the wild variety of the plant, but its cultivars. This is because the leaves of the wild type of water pepper are extremely pungent. The essential oil yielded by wild water pepper causes irritation to the skin. In addition, tissues of the wild variety also enclose various acids, such as formic acid. As a result, wild water pepper is not palatable to livestock. The tender reddish sprouts of water pepper are employed in the form of sashimi garnish in Japan, where they are called beni-tade (meaning red water pepper). Sometimes, people also add the water pepper seeds to wasabi.
In Japan, the sauce prepared from water pepper is called Tade-zu (literally meaning water pepper vinegar). Traditionally, Tade-zu is prepared from finely sliced leaves of water pepper, which are soaked in vinegar and a little quantity of steamed rice. On some occasions, people in Japan also add the juice extracted from kabosu. Water pepper sauce is traditionally used to go together with grilled freshwater fish. However, generally it does not go with any other type of grilled fish.
Habitat and cultivation
Water pepper is native to places having temperate climatic conditions. In China and Japan, people cultivate this plant owing to the peppery flavour of its leaves. In these countries it is used as an ingredient in spice mixes. In addition, water pepper is also cultivated in many regions of Europe. This herb has a preference for damp soil. Usually, the leaves of water pepper are used fresh. When you chew this plant’s leaves for some time, it will cause a prickling sensation in the mouth. These leaves generate a characteristic heat that is comparable to pepper and chilli.
This is an annually growing plant. If you want to grow water pepper outdoors, you should sow its seeds March onwards when the temperature has risen favourably. Prior to sowing, it is necessary to soak the seeds for some time in 2°C-4°C cold water. Soaking the seeds in cold water will enhance the rate of their germination. Water pepper has a preference for sunny locations having some moisture in the atmosphere. It also thrives on the shore of lakes and other water bodies.
Chemical examination of water pepper (hydropiper) has revealed that the plant encloses many active compounds. Aside from containing two bicyclic sesquiterpenoids, this herb also encloses polygodial as well as waburganal. The edibility and pungent flavour of this herb are attributed to these compounds. In addition, water pepper also encloses a compound called rutin, which is responsible for its bitter impression.
Water pepper also encloses 0.5 per cent essential oil comprising monoterpenoids and sesquiterpenoids, which include 1.4-cineol, α-humulene, α-pinene, β-caryophyllene, β-pinene and trans-β-bergamotene. It has been found that the plant encloses also carboxylic acids such as caproic acid, valleric and cinnamic acids as well as their esters in trace amounts.