''Polygonum aviculare'' or common knotgrass is a plant related to

buckwheat Buckwheat (''Fagopyrum esculentum'') or common buckwheat is a flowering plant in the knotweed family Polygonaceae cultivated for its grain-like seeds and as a cover crop. Buckwheat originated around the 6th millennium BCE in the region of what ...

and

dock The word dock () in American English refers to one or a group of human-made structures that are involved in the handling of boats or ships (usually on or near a shore). In British English, the term is not used the same way as in American Engl ...

. It is also called prostrate knotweed, birdweed, pigweed and lowgrass. It is an annual found in fields and wasteland, with white flowers from June to October. It is widespread across many countries in temperate regions, apparently native to Eurasia, naturalized in temperate parts of the Southern Hemisphere.Flora of China, ''Polygonum aviculare'' Linnaeus, 1753. 萹蓄 bian xu
/ref>Flora of North America, ''Polygonum aviculare'' Linnaeus, 1753. Doorweed, knotgrass, renouée des oiseaux
/ref>

Description

Common knotgrass is an annual, low-prostrate herb with semi-erect, branching stems, which forms patches up to about 2 m across as it matures. It has alternate linear-lanceolate leaves which are longer (7-15 mm) on the main stems than on the branches (3-5 mm). The whole plant is hairless and green, although it may appear mealy due to a powdery mildew, which can give the leaves a whitish appearance. The leaves fall early, especially on the main stem. The leaf stalks (petioles) are up to 5 mm long or sometimes absent. Above each leaf there is an ochrea, which is a translucent papery

stipule In botany, a stipule is an outgrowth typically borne on both sides (sometimes on just one side) of the base of a leafstalk (the petiole (botany), petiole). They are primarily found among dicots and rare among monocots. Stipules are considered part ...

that surrounds the stem. The inflorescences occur in the leaf axils and consist of a group of 1-6 flowers, each on a very short (1 mm) stalk (pedicel). The flowers are green with white or pink margins, ranging in size from 2 to 4.5 mm. Each flower has five overlapping

perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower. It is a structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals) or tepal ...

segments, fused into a cup for about a third of their length, with 8 stamens and 3 carpels. The fruit is a dark brown nut 1.5 - 3.5 mm long with 3 concave sides and a dull, leathery sheen. When ripe it is enclosed in the perianth. The seeds need light to germinate which is why this plant appears in disturbed soil in locations where its seeds may have lain dormant for years.

Taxonomy

The name "Polygonum" comes from the Ancient Greek for "many knees", in reference to the prominent joints (nodes) along the stem. The specific epithet "aviculare" means "little bird", possibly because the fruits resemble a bird's beak or an egg. Common names include birdweed, pigweed and lowgrass. ''Polygonum aviculare'' has a wide distribution as an arable weed and plant of fields, shingle, sand, roadsides, yards and waste places. There is much morphological variation among different populations and several different sub-species are recognized: * ''Polygonum aviculare ''subsp''. aviculare'' – very widespread *''Polygonum aviculare'' subsp. ''boreale'' (Lange) Karlsson – Greenland, Labrador, Newfoundland, Scandinavia *''Polygonum aviculare'' subsp. ''buxiforme'' (Small) Costea & Tardif – North America * ''Polygonum aviculare'' subsp. ''depressum'' (Meisn.) Arcang. – Europe, North America *''Polygonum aviculare'' var. ''fusco-ochreatum'' (Kom.) A.J.Li – northeastern China, Russian Far East *''Polygonum aviculare'' subsp. ''neglectum'' (Besser) Arcangeli – Europe, North America * ''Polygonum aviculare ''subsp''. rurivagum'' (Jord. ex Boreau) Berher – Europe, North America

Distribution

Widespread and common in

Great Britain Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...

Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...

,Clapham, A.R. , Tutin, T.G. and Warburg, E.F. 1968. ''Excursion Flora of the British Isles''. Cambridge Press. Parnell, J. and Curtis, T. 2012. ''Webb's An Irish Flora.'' Cork University Press. and

Scandinavia Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...

Habitat

It is common on roadsides and arable ground in the British Isles.

Ecology

The ecological requirements of this species are fairly modest. Its Ellenberg values in Britain are L = 7, F = 5, R = 6, N = 7, and S = 0, which shows that it prefers average light, moisture and fertility, neutral pH and non-saline conditions. However, it can be found on beaches so it must be tolerant of occasional immersion in seawater. Many species of insects feed on knotgrass, including the eponymous Knot Grass moth, ''Acronicta rumicis'', whose larvae are phytophagous on the leaves. The UK'
Database of Insects and their Food Plants
lists 113 species which are known to feed on this plant in Britain, of which 10 are

beetle Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...

s, 2 are

flies Flies are insects of the Order (biology), order Diptera, the name being derived from the Ancient Greek, Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwin ...

, 8 are

Hemiptera Hemiptera (; ) is an order of insects, commonly called true bugs, comprising more than 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from ...

(bugs and aphids), and the remaining 93

Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...

(butterflies and moths).

Chemistry

''Polygonum aviculare'' contains the flavonols avicularin, myricitrin and juglanin. The flavanoids astragalin and betmidin, and the lignan aviculin have also been found. The

diterpene Diterpenes are a class of terpenes composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate being a primary ...

alkaloid Alkaloids are a broad class of natural product, naturally occurring organic compounds that contain at least one nitrogen atom. Some synthetic compounds of similar structure may also be termed alkaloids. Alkaloids are produced by a large varie ...

panicudine is another known component.

Fossil record

One fossil fruit of ''Polygonum aviculare'' has been extracted from

borehole A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petr ...

samples of the

Middle Miocene The Middle Miocene is a sub-epoch of the Miocene epoch (geology), epoch made up of two Stage (stratigraphy), stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene. The sub-epoch lasted from 15.97 ± 0. ...

fresh water deposits in Nowy Sacz Basin, West Carpathians,

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...

Cuisine

It formed a traditional ingredient in porridge consumed by Germanic peoples of western Europe, and has been found in numerous autopsies of peat bodies, including the Tollund Man. In Vietnam, where it is called ''rau đắng'', it is widely used to prepare soup and hot pot, particularly in the southern region.

In culture

In the Harry Potter novels, knotgrass is an ingredient in the magic potion polyjuice.

References

External links

photo of herbarium specimen collected in Nuevo León in Mexico in 1989
* Howard, Michael. ''Traditional Folk Remedies'', (Century, 1987); page 162. {{Taxonbar, from=Q242573 aviculare Medicinal plants Flora of Northern America Flora of Europe Flora of temperate Asia Flora of tropical Asia Plants described in 1753 Taxa named by Carl Linnaeus