# Knotgrass (Polygonum aviculare)

*Centinode, ninety-knot, nine-joints, allseed, bird’s tongue, sparrow tongue, red robin, armstrong, cowgrass, hogweed, swine’s grass, swynel grass; the male *polugonon* of Dioscorides; *Polygonum aviculare* L.; in pharmacy *Polygoni avicularis herba**

**Known today as.** *Polygonum aviculare*, of the family Polygonaceae, a common weed of arable land, waste ground, and roadsides the world over. Its much-branched, usually prostrate stems have swollen joints, “hence the common names, Nine-joints, Ninety-knots,” and the small narrow leaves issue from white, shining, torn sheaths; the flowers are minute, usually pinkish. Grieve derives *aviculare* from the Latin for a little bird, many small birds feeding on its seeds, and ‘armstrong’ from the difficulty of pulling it up.

Kind: Plant

> **Caution.** Not recommended under twelve. For the urinary use plenty of fluid is needed, so not where a reduced fluid intake is advised, as in severe heart disease; see a doctor if fever, painful urination, spasms, or blood in the urine appear, or if cold or throat symptoms worsen.

## What was it used for?

An astringent herb for bleeding, fluxes, and the urine. Dioscorides gave its juice as astringent and cooling for those spitting blood, discharges of the bowel, and slow painful urination. Culpeper made its juice “most effectual to stay bleeding of the mouth,” and of the nose when applied to the temples or squirted into the nostrils, and found it singularly good to provoke urine and expel gravel and stone. Grieve sums it up as useful in diarrhoea, bleeding piles, “and all haemorrhages,” formerly much used as a wound herb and styptic.

## What does modern science say?

The European Medicines Agency’s herbal committee accepts the herb as a traditional herbal medicine, “exclusively based upon long-standing use,” for the symptoms of the common cold, for minor inflammations of the mouth or throat, and to increase the amount of urine and flush the urinary tract in minor urinary complaints (monograph of 2016). Its assessment report finds 3.5 to 4 per cent of tannins with phenolic acids, coumarins, and the lignan aviculin.

## Pharmacognosy and toxicology

- **tannins**: 3.5 to 4 per cent
- **aviculin**: a lignan
- **coumarins**: 

**Mechanism.** Not established in the sources read for this entry.

**Standing.** European Union herbal monograph (2016): traditional use, “exclusively based upon long-standing use,” for symptoms of the common cold, minor mouth and throat inflammation, and minor urinary complaints.

## What lore surrounds it?

Gerard, as Grieve quotes him, says it “is given to swine with good successe when they are sicke and will not eat their meate,” whence Swine’s Grass. Shakespeare’s ‘hindering knotgrass’ in *A Midsummer Night’s Dream*, Grieve explains, refers to the belief that its decoction stunted the growth of children and young animals.

## What did the older authorities say?

**Culpeper, *The Complete Herbal* (1653).** “Saturn seems to me to own the herb, and yet some hold the Sun; out of doubt ’tis Saturn.” Its distilled water he counted “one of the most sovereign remedies to cool all manner of inflammations,” for hot swellings, gangrene, and foul ulcers, and the juice dropped into the ears to cleanse them.

**Dioscorides, *De materia medica* 4.4.** The male *polugonon*, which the modern translators identify with knotgrass, is a tender herb of many slender jointed branches creeping along the earth like grass, with seed by every leaf, “which is why it is called the male.”

## Sources

- Grieve, M. *A Modern Herbal*, “Knotgrass.” As published on botanical.com.
- Culpeper, N. *The Complete Herbal*, “Knotgrass.” Project Gutenberg, 49513.
- Dioscorides. *De materia medica*, 4-4, in the modern English version of T. A. Osbaldeston and R. P. A. Wood (Johannesburg: Ibidis, 2000), after Goodyer’s translation of 1655. Internet Archive.
- European Medicines Agency, Committee on Herbal Medicinal Products. *European Union herbal monograph on Polygoni avicularis herba (Knotgrass herb)*. EMA/HMPC/143658/2015, 5 April 2016.
- European Medicines Agency, Committee on Herbal Medicinal Products. *Assessment report on Polygoni avicularis herba*. EMA/HMPC/143659/2015, 5 April 2016.
- European Medicines Agency, Committee on Herbal Medicinal Products. *European Union herbal monograph on Polygoni avicularis herba (Knotgrass herb)*. EMA/HMPC/143658/2015, 5 April 2016.
- European Medicines Agency, Committee on Herbal Medicinal Products. *Assessment report on Polygoni avicularis herba*. EMA/HMPC/143659/2015, 5 April 2016.

---

*Knotgrass.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-17. The Thinking Press. https://thethinkingpress.org/materia-medica/knotgrass

Historical description, not medical advice.