Polygonum aviculare or Common Knotgrass is a plant related to buckwheat

Buckwheat

Buckwheat refers to a variety of plants in the dicot family Polygonaceae: the Eurasian genus Fagopyrum, the North American genus Eriogonum, and the Northern Hemisphere genus Fallopia. Either of the latter two may be referred to as "wild buckwheat"...

 and dock. It is also called birdweed, pigweed and lowgrass. It is an annual found in fields and wasteland, with white flowers from June to October.

Herbalism and folklore

Nicholas Culpeper

Nicholas Culpeper

Nicholas Culpeper was an English botanist, herbalist, physician, and astrologer. His published books include The English Physician and the Complete Herbal , which contain a rich store of pharmaceutical and herbal knowledge, and Astrological Judgement of Diseases from the Decumbiture of the Sick ,...

 states that the plant is ruled astrologically by Saturn and Capricorn. He also recommended knotweed to cure the spitting of blood. Modern herbalists use it to treat dysentery

Dysentery

Dysentery is an inflammatory disorder of the intestine, especially of the colon, that results in severe diarrhea containing mucus and/or blood in the faeces with fever and abdominal pain. If left untreated, dysentery can be fatal.There are differences between dysentery and normal bloody diarrhoea...

, excessive menstrual flow, lung disorders, bronchitis

Bronchitis

Acute bronchitis is an inflammation of the large bronchi in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum production, and shortness of breath and wheezing related to the obstruction of the inflamed airways...

 and jaundice

Jaundice

Jaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...

, and gall

Gallstone

A gallstone is a crystalline concretion formed within the gallbladder by accretion of bile components. These calculi are formed in the gallbladder, but may pass distally into other parts of the biliary tract such as the cystic duct, common bile duct, pancreatic duct, or the ampulla of...

 and kidney stones. Not all of these uses are supported by scientific evidence.} recommended knotweed to cure the spitting of blood. Modern herbalists use it to treat dysentery

Dysentery

Dysentery is an inflammatory disorder of the intestine, especially of the colon, that results in severe diarrhea containing mucus and/or blood in the faeces with fever and abdominal pain. If left untreated, dysentery can be fatal.There are differences between dysentery and normal bloody diarrhoea...

, excessive menstrual flow, lung disorders, bronchitis

Bronchitis

Acute bronchitis is an inflammation of the large bronchi in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum production, and shortness of breath and wheezing related to the obstruction of the inflamed airways...

 and jaundice

Jaundice

Jaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...

, and gall

Gallstone

A gallstone is a crystalline concretion formed within the gallbladder by accretion of bile components. These calculi are formed in the gallbladder, but may pass distally into other parts of the biliary tract such as the cystic duct, common bile duct, pancreatic duct, or the ampulla of...

 and kidney stones. Not all of these uses are supported by scientific evidence. The plant is an astringent

Astringent

An astringent substance is a chemical compound that tends to shrink or constrict body tissues, usually locally after topical medicinal application. The word "astringent" derives from Latin adstringere, meaning "to bind fast"...

, coagulant

Coagulant

Coagulant can refer to:* flocculation* coagulation agent...

, diuretic

Diuretic

A diuretic provides a means of forced diuresis which elevates the rate of urination. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way.- Medical uses :...

 and expectorant.

Cuisine

In Vietnam

Vietnam

Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

, where it is called rau đắng, it is widely used to prepare soup

Soup

Soup is a generally warm food that is made by combining ingredients such as meat and vegetables with stock, juice, water, or another liquid. Hot soups are additionally characterized by boiling solid ingredients in liquids in a pot until the flavors are extracted, forming a broth.Traditionally,...

 and hot pot

Hot pot

Hot pot , less commonly Chinese fondue or steamboat, refers to several East Asian varieties of stew, consisting of a simmering metal pot of stock at the center of the dining table. While the hot pot is kept simmering, ingredients are placed into the pot and are cooked at the table...

, particularly in the South region.

Subspecies

• Polygonum aviculare subsp. aviculare
• Polygonum aviculare subsp. depressum (Meisn.) Arcang.
• Polygonum aviculare subsp. rurivagum (Jord. ex Boreau) Berher in Louis