Water pepper: beneficial properties and uses

Dr. Boris Wydoff

Water pepper, or pepper knotweed, is an annual plant from the Buckwheat family. According to herbal medicine reference books, it is known primarily as a plant used in the form of water and alcohol extracts for hemostatic purposes. Herbal manuals also describe traditional ways of using the plant and rules for distinguishing it from similar knotweeds.

What kind of plant is it?

Water pepper (*Persicaria hydropiper* (L.) Spach, also *Polygonum hydropiper* L.) is an annual herbaceous plant from the Buckwheat family. Reference books describe it as a plant reaching approximately 30–70 cm in height.

The stem is upright or ascending. It branches from the base. The stem is usually reddish, hollow, and divided by nodes. At the points where the leaves attach are ochreas — parts of the plant that surround the stem.

The leaves are lance-shaped. Their length is about 3–10 cm. The underside of the leaf may be slightly hairy. At the base there is a brownish ochrea that surrounds the stem. On the upper side of the leaf, translucent dots can be seen. In reference books, they are described as dots of essential oil glands. The flowers of water pepper are small. They have a greenish or whitish-pink color. The flowers are collected into narrow, interrupted, drooping racemes.

The fruit of the plant is a small black three-sided nutlet about 2–3 mm long. Flowering begins at the end of June and continues until September. The fruits ripen from July to October.

When getting to know the plant, I advise paying attention to several signs at once. One external feature alone may not be enough. This is especially important because other types of knotweeds can grow near water pepper.

What signs help identify the plant?

To identify water pepper, it is useful to examine the whole plant rather than a single leaf or flower. The ochrea at the base of the leaf is brownish and surrounds the stem. The stem itself is reddish, hollow, and knotted, while the inflorescences do not form a dense spike.

There is another feature noted in reference books: translucent dots of essential oil glands can be seen on the leaves of water pepper. Together with the leaf shape and the structure of the inflorescences, this feature helps clarify the identification.

The taste of the fresh plant is especially characteristic. It is pungent, bitter, and peppery. This particular feature is connected with the name “water pepper.”

Where does water pepper grow?

Water pepper is associated with moist places. According to reference books, it can be found in marshy meadows, floodplains, near rivers, ponds, swamps, and lakes. The plant also occurs near irrigation canals and on irrigated lands. Sometimes it grows as a weed and forms quite large patches.

The range of water pepper is wide. It is distributed from Western Europe to the Far East, from northern regions of Europe to southern territories, including Indonesia and the Philippines. It is also recorded in northern Africa and Australia.

Why does the growing location help with identification?

Water pepper belongs to plants of moist habitats. In literature, it is described among representatives of a special “mermaid’s pharmacy” — moisture-loving and aquatic plants, among which medicinal species can also be found.

However, the growing location alone is not enough. Different knotweed species can grow at the same time on riverbanks and wet meadows. Therefore, wet soil, a riverbank, or a marshy area only suggest where to look for the plant, but do not confirm its species.

How to distinguish water pepper from other knotweeds?

When harvesting the plant, it is important to identify the species correctly. Water pepper can grow next to other knotweeds that look similar. Water pepper has characteristic features. These include a reddish hollow stem, lance-shaped leaves with a brownish ochrea at the base, and narrow, interrupted, drooping inflorescences. The main feature often mentioned in reference books is the taste of the fresh plant. It is pungent, bitter, and peppery. This characteristic gave the plant its name “water pepper.”

The name itself can cause confusion. Water pepper is also known by the folk name “pochechuynaya grass.” This is connected with the old name for hemorrhoids — “pochechuy.” At the same time, there is another species — Persian knotweed (*Polygonum persicaria* L.), which is also connected with this name and grows in similar places.

Therefore, when harvesting, one should not rely only on the folk name. The botanical features of the plant must be considered.

Which differences are especially important?

Reference books note that other knotweed species growing in the same habitats often have dense spike-like inflorescences. Their flowers may be pink, white, or light green. In water pepper, by contrast, the inflorescences are narrow, interrupted, and drooping.

For distinguishing it from Persian knotweed (*Polygonum persicaria* L.), the appearance of the leaves is important. Persian knotweed usually has a black-brown spot on the leaves. Its ochrea has short, stiff, appressed hairs and long eyelashes along the edge.

A botanical identification table also lists rough knotweed (*Polygonum scabrum* Moench). Its ochrea is hairless, with short eyelashes along the edge, and the underside of the leaves may have yellowish-brown shiny glands. The flowers of this species are usually white.

There is also small knotweed (*Polygonum minus* Huds.), whose perianth has no glands, while the ochrea edge is long-fringed and covered with long hairs.

Such features are especially important during independent harvesting. In nature, plants can look very similar, although their chemical composition and active substance content differ.

What is water pepper useful for?

The main area of use of water pepper is connected with hemostatic properties.

According to herbal medicine reference books, water pepper is used in official medicine in the form of water and alcohol extracts. Reference literature describes the use of such forms for uterine, menstrual, hemorrhoidal, gastric, and other bleeding.

Reference books also describe the preparation “Hydropiperin.” It is indicated as increasing blood clotting and being used for uterine bleeding of various origins.

In folk medicine, water pepper infusion and tincture were traditionally used for uterine bleeding, heavy and painful menstruation, after abortions or childbirth, as well as for coughing up blood, gastric, and hemorrhoidal bleeding.

I always remind people: bleeding is a symptom, not an independent diagnosis. The cause should be assessed by a doctor.

What is known about medicinal use?

One reference book specifically connects the use of water pepper with obstetric and gynecological practice. It describes the use of the plant for postpartum uterine bleeding, uterine subinvolution, and prolonged and heavy menstruation.

It also mentions use for bleeding from small vessels and capillaries of the stomach and intestines, as well as for minor hemorrhoidal bleeding.

In official medicine, water pepper is known as a medicinal plant, not only as a traditional remedy. Literature mentions plant extract included in anti-hemorrhoid suppositories “Anestezol.”

These details describe the use of medicinal forms of the plant in medical practice and do not mean that fresh herb or a self-made tincture can be used instead of examination and prescribed treatment.

How is the plant used for different conditions?

According to reference books, the use of water pepper is mainly associated with the circulatory system and conditions where the plant’s hemostatic effect has been described. Herbal manuals also describe external use of the plant. Infusion and herb were used for some skin problems: rashes, abscesses, wounds, and other skin lesions. Crushed herb was used for old bruises. In folk practice, fresh crushed herb was applied to the back of the head for headaches as an external irritant instead of mustard plasters.

This method should be approached with caution. Fresh herb can irritate the skin, and in some cases contact may cause blisters. The cause of a headache also requires attention if the symptom repeats or has an unusual character.

What external methods are described in herbal manuals?

External use in old folk practice was quite varied. Water pepper was used for rashes, abscesses, wounds, and so-called “wild flesh.” Sources also mention the use of crushed herb for old bruises and for removing freckles.

Fresh crushed herb was applied to the back of the head for headaches. This method was considered specifically an external irritant effect and was compared with the use of mustard plasters. At the same time, external use does not make the plant harmless for the skin. If severe irritation or blisters appear, contact with the plant should be stopped.

How to brew water pepper?

Reference literature describes water and alcohol extracts of the plant. Folk medicine mentions infusion and tincture of water pepper. However, a safe modern medicinal dose for independent use has not been established. Therefore, I do not recommend making more concentrated preparations yourself or changing preparation methods. For medicinal use, the form of the preparation and the situation in which it is used are important. This is especially significant when combined with other medicines.

What medicinal forms are described?

In different sources, water pepper appears as a plant used to obtain water and alcohol extracts. Folk medicine separately mentions infusion and tincture. In official medical practice, plant extract was used. Reference books also mention the name “Hydropiperin,” which is attributed with an effect on blood clotting. These details should not be turned into a home preparation scheme with arbitrary concentration. The composition and strength of a self-made remedy may differ from a standardized preparation.

How is water pepper collected and stored?

Only a correctly identified plant should be harvested. Water pepper often grows near other knotweed species, so an identification mistake may result in obtaining different plant material.

During collection, look at the combination of features: the structure of the stem, the shape of the leaves, the characteristics of the inflorescences, and the plant’s characteristic taste. Unknown plants should not be collected only by photograph or general similarity. Different species may have different properties and compositions.

The wet places where water pepper grows are not, by themselves, a guarantee of correct identification. The name of the location and the appearance of the vegetation do not replace checking the plant’s features.

Why is correct identification especially important?

Literature on medicinal plant collection specifically emphasizes the problem of external similarity. In nature, many plants look alike but differ in chemical composition and active substance content.

Water pepper is given as one example. It can easily be confused with other knotweed species that have no medicinal significance.

Therefore, before harvesting, it is necessary to know the plant well and be able to distinguish it from related species. For water pepper, the combination of features is especially important: a reddish hollow stem, lance-shaped leaves, a brownish ochrea, interrupted drooping racemes, and a characteristic pungent taste.

How to find water pepper (pepper knotweed) abroad

Abroad, this plant may appear under different names:

• USA: water pepper, also marshpepper knotweed.
• Germany: Wasserpfeffer; the herb may be sold as Wasserpfefferkraut.
• France: poivre d’eau or renouée poivre-d’eau.
• Latin: *Persicaria hydropiper*; the synonym *Polygonum hydropiper* may also be listed on the label.

When buying, look specifically for the herb or aerial parts of the plant (Kraut, parties aériennes). Products available for sale include:

• chopped dried herb without individual tea bags;
• tinctures or drops — in Germany and France;
• capsules — for buyers in the USA, but their availability is less confirmed.

Where to look:

• in the USA — with online herb and supplement sellers;
• in Germany — at Apotheke or with online herb and tea sellers;
• in France — in online-herboristerie shops or marketplaces.

Check the label for *Persicaria hydropiper* or *Polygonum hydropiper* and the indication herb/aerial parts. A similar name alone is not enough. Also check whether the product is classified as Arzneitee or as a food herbal infusion. Different countries have their own rules: for example, in the USA supplements are regulated by the FDA, but do not receive prior FDA approval before being sold.

Water pepper contraindications and precautions

According to current data, there are not enough clinical studies on *Persicaria hydropiper* to establish a safe medicinal dose and a complete list of possible interactions. If the plant has caused a reaction before, it should not be used. Contact with fresh herb may irritate the skin, and in some cases may cause blisters. Taking water pepper together with medicines requires caution. Confirmed clinical interactions are insufficient, so combining herbal preparations with medicines is better discussed with a doctor or pharmacist.

Medicinal use should be avoided during pregnancy. Studies of root extracts in rats showed estrogenic and antifertility effects, but these results cannot be directly transferred to humans.

During breastfeeding, there is insufficient safety data. Children should not use medicinal preparations from water pepper without professional advice.

In laboratory studies, individual leaf fractions gave mixed results in genotoxicity tests. High doses of injectable extracts caused death in mice. These data do not allow determining a specific human dose, but they require caution.

When is a doctor needed?

Bleeding requires specialist attention, especially if the cause is unknown, it repeats, or is accompanied by worsening health. A doctor should be consulted for pronounced weakness, dizziness, and other unusual symptoms. Before using water pepper, possible allergies and previous reactions to the plant should be considered. During pregnancy and breastfeeding, medicinal use should be avoided. If a person takes medicines, combining them with an herbal preparation should be discussed with a doctor or pharmacist.

For chronic diseases, consultation with a specialist is necessary. Children should not use water pepper preparations without professional advice.

Boris Wydoff — naturopath and author, Ph.D. in nutrition. For over fifty years I have helped people restore health through nutrition, cleansing and the power of the mind — in Europe, America and Asia. About the author →

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