Polygonum

Polygonum is a genus of about 130 species of flowering plants in the buckwheat and knotweed family Polygonaceae. Common names include knotweed and knotgrass (though the common names may refer more broadly to plants from Polygonaceae). In the Middle English glossary of herbs Alphita (c. 1400–1425), it was known as ars-smerte. There have been various opinions about how broadly the genus should be defined. For example, buckwheat (Fagopyrum esculentum) has sometimes been included in the genus as Polygonum fagopyrum. Former genera such as Polygonella have been subsumed into Polygonum; other genera have been split off.

The genus primarily grows in northern temperate regions. The species are very diverse, ranging from prostrate herbaceous annual plants to erect herbaceous perennial plants.

Polygonum species are occasionally eaten by humans, and are used as food plants by the larvae of some Lepidoptera species – see list. Most species are considered weeds in Europe and North America.

Description
When the genus is defined narrowly, Polygonum species are annual or perennial herbaceous plants, rarely shrubby, with much branched stems. The leaves are arranged alternately, usually less than 2 cm long, with a length greater than the width. They have a membranous ochrea (a sheath around the stem nodes). The flowers are usually bisexual, rarely unisexual, and have five (occasionally four) tepals, the outer being slightly different from the inner ones. There are usually four to six stamens and three (rarely two) styles. The fruit is three-sided.

Taxonomy
The genus Polygonum was first described by Carl Linnaeus in 1754. The genus name is usually said to be from the Greek πολυ- (poly-, 'many') and γόνυ (gonu, 'knee' or 'joint'), in reference to the swollen jointed stem. However, long before Linnaeus, the name was used in Greek and Latin for a plant used medically. Discussing the plant he knew as polygonum in 1655, Matthias Martinius referred to Scribonius Largus (who wrote a list of prescriptions around 47 AD) and gave an alternative etymology, based on γόνος (gonos, 'offspring', 'seed'), the meaning of the name then being the Latin foecundus, i.e. 'fecund', 'with many offspring'. The Flora of North America says that a derivation meaning 'many seeds' is the "grammatically correct interpretation".

Many members of the family Polygonaceae that are now placed in separate genera were at one time or other placed in Polygonum, including species of Fagopyrum, Fallopia, Persicaria and Reynoutria, and older sources frequently use much wider definitions of the genus. Molecular phylogenetic studies, particularly in the 21st century, have led to major changes. Clarifying the circumscription of genera split from Polygonum was described in 2015 as "still ongoing".

Classification and phylogeny
Polygonum is placed in the tribe Polygoneae of the subfamily Polygonoideae. Within the tribe, it is most closely related to the genera Duma and Atraphaxis, forming the so-called "DAP clade".

Species
Between 65 and 300 species have been recognised at various times, depending on the circumscription of the genus. A number of species that had been included in Polygonum have been moved into several other genera, including Bistorta, Fagopyrum, Fallopia, Koenigia, Persicaria and Reynoutria. Other genera, such as Polygonella, have been subsumed into Polygonum.

, Plants of the World Online accepted 129 species.


 * Polygonum acerosum Ledeb. ex Meisn.
 * Polygonum acetosum M.Bieb.
 * Polygonum achoreum S.F.Blake
 * Polygonum adenopodum Sam.
 * Polygonum afromontanum Greenway
 * Polygonum agreste Sumnev.
 * Polygonum ajanense (Regel & Tiling) Grig.
 * Polygonum albanicum Jáv.
 * Polygonum americanum (Fisch. & C.A.Mey.) T.M.Schust. & Reveal
 * Polygonum amgense Michaleva & Perfiljeva
 * Polygonum arenarium Waldst. & Kit.
 * Polygonum arenastrum Boreau
 * Polygonum argyrocoleon Steud. ex Kunze
 * Polygonum articulatum L.
 * Polygonum austiniae Greene
 * Polygonum aviculare L.
 * Polygonum balansae Boiss.
 * Polygonum basiramia (Small) T.M.Schust. & Reveal
 * Polygonum bellardii All.
 * Polygonum biaristatum Aitch. & Hemsl.
 * Polygonum bidwelliae S.Watson
 * Polygonum bolanderi W.H.Brewer ex A.Gray
 * Polygonum boreale (Lange) Small
 * Polygonum bornmuelleri Litv.
 * Polygonum bowenkampii Phil.
 * Polygonum brasiliense K.Koch
 * Polygonum californicum Meisn.
 * Polygonum cascadense W.H.Baker
 * Polygonum caspicum Kom.
 * Polygonum ciliinode Michx. – fringed black bindweed, mountain bindweed
 * Polygonum cognatum Meisn.
 * Polygonum corrigioloides Jaub. & Spach
 * Polygonum deciduum Boiss. & Noë
 * Polygonum delopyrum T.M.Schust. & Reveal
 * Polygonum dentoceras T.M.Schust. & Reveal
 * Polygonum douglasii Greene
 * Polygonum effusum Meisn.
 * Polygonum engelmannii Greene
 * Polygonum equisetiforme Sm.
 * Polygonum erectum L.
 * Polygonum exsertum Small
 * Polygonum fibrilliferum Kom.
 * Polygonum fimbriatum Elliott
 * Polygonum floribundum Schltdl. ex Spreng.
 * Polygonum fowleri B.L.Rob.
 * Polygonum fragile Sumnev.
 * Polygonum glaucum Nutt.
 * Polygonum gussonei Tod.
 * Polygonum heterophyllum Sol. ex Meisn.
 * Polygonum heterosepalum M.Peck & Ownbey
 * Polygonum hickmanii H.R.Hinds & Rand.Morgan
 * Polygonum huananense A.J.Li
 * Polygonum humifusum C.Merck ex K.Koch
 * Polygonum icaricum Rech.f.
 * Polygonum idaeum Hayek
 * Polygonum imberbe Sol. ex G.Forst.
 * Polygonum inflexum Kom.
 * Polygonum istanbulicum M.Keskin
 * Polygonum jaxarticum Sumnev.
 * Polygonum korotkovae Sumnev.
 * Polygonum kudriaschevii Vassilkovsk.
 * Polygonum lacerum Kunth
 * Polygonum liaotungense Kitag.
 * Polygonum longiocreatum Bartlett
 * Polygonum longipes Halácsy & Charrel
 * Polygonum majus (Meisn.) Piper
 * Polygonum marinense T.R.Mert. & P.H.Raven
 * Polygonum maritimum L.
 * Polygonum mezianum H.Gross
 * Polygonum minimum S.Watson
 * Polygonum molliiforme Boiss.
 * Polygonum myrtillifolium Kom.
 * Polygonum nesomii T.M.Schust. & Reveal
 * Polygonum nuttallii Small
 * Polygonum oxanum Kom.
 * Polygonum oxyspermum C.A.Mey. & Bunge
 * Polygonum palastinum Zohary
 * Polygonum papillosum Hartvig
 * Polygonum parksii (Cory) T.M.Schust. & Reveal
 * Polygonum paronychia Cham. & Schltdl.
 * Polygonum paronychioides C.A.Mey.
 * Polygonum parryi Greene
 * Polygonum patulum M.Bieb.
 * Polygonum peruvianum Meisn.
 * Polygonum pinicola T.M.Schust. & Reveal
 * Polygonum plebeium R.Br.
 * Polygonum polycnemoides Jaub. & Spach
 * Polygonum polygaloides Meisn.
 * Polygonum polygamum Vent.
 * Polygonum polyneuron Franch. & Sav.
 * Polygonum pringlei Small
 * Polygonum pulvinatum Kom.
 * Polygonum ramosissimum Michx.
 * Polygonum rectum (Chrtek) H.Scholz
 * Polygonum recumbens Royle ex Bab.
 * Polygonum rigidum Skvortsov
 * Polygonum romanum Jacq.
 * Polygonum rottboellioides Jaub. & Spach
 * Polygonum rupestre Kar. & Kir.
 * Polygonum rurivagum Jord. ex Boreau
 * Polygonum sabulosum Vorosch.
 * Polygonum salsugineum M.Bieb.
 * Polygonum sanguinaria Remy
 * Polygonum sawatchense Small
 * Polygonum schistosum Czukav.
 * Polygonum scoparium Req. ex Loisel.
 * Polygonum sericeum Pall.
 * Polygonum serpyllaceum Jaub. & Spach
 * Polygonum shastense W.H.Brewer ex A.Gray
 * Polygonum simlense Royle ex Bab.
 * Polygonum smallianum T.M.Schust. & Reveal
 * Polygonum spergulariiforme Meisn. ex Small
 * Polygonum striatulum B.L.Rob.
 * Polygonum stypticum Cham. & Schltdl.
 * Polygonum subaphyllum Sumnev.
 * Polygonum tenoreanum E.Nardi & Raffaelli
 * Polygonum tenue Michx.
 * Polygonum tenuissimum A.I.Baranov & Skvortsov ex Vorosch.
 * Polygonum thymifolium Jaub. & Spach
 * Polygonum tiflisiense Kom.
 * Polygonum tubulosum Boiss.
 * Polygonum turgidum Thuill.
 * Polygonum turkestanicum Sumnev.
 * Polygonum undulatum (L.) P.J.Bergius
 * Polygonum utahense Brenckle & Cottam
 * Polygonum valerii A.K.Skvortsov
 * Polygonum volchovense Tzvelev
 * Polygonum vvedenskyi Sumnev.
 * Polygonum zaravschanicum Zakirov

Reclassified species
Many species formerly placed in Polygonum have been moved to other genera in the subfamily Polygonoideae. Some synonyms are listed below.

Polygonum species that have been reclassified as Bistorta

 * Polygonum amplexicaule → Bistorta amplexicaulis
 * Polygonum bistorta – bistort → Bistorta officinalis
 * Polygonum bistortoides Pursh – American bistort, western bistort, smokeweed or mountain meadow knotweed → Bistorta bistortoides
 * Polygonum tenuicaule Bisset & S.Moore → Bistorta tenuicaulis
 * Polygonum viviparum – alpine bistort → Bistorta vivipara

Polygonum species that have been reclassified as Fagopyrum

 * Polygonum fagopyrum L. – buckwheat → Fagopyrum esculentum

Polygonum species that have been reclassified as Fallopia

 * Polygonum aubertii L.Henry → Fallopia aubertii
 * Polygonum baldschuanicum Regel – Russian vine → Fallopia baldschuanica
 * Polygonum convolvulus L. – black bindweed, wild buckwheat → Fallopia convolvulus
 * Polygonum dumetorum L. → Fallopia dumetorum
 * Polygonum scandens L. → Fallopia scandens

Polygonum species that have been reclassified as Koenigia

 * Polygonum alpinum → Koenigia alpina
 * Polygonum campanulatum – lesser knotweed, bellflower smartweed → Koenigia campanulata
 * Polygonum davisiae W.H. Brewer ex A. Gray and Polygonum newberryi Small → Koenigia davisiae
 * Polygonum molle → Koenigia mollis
 * Polygonum polystachyum Wall. ex Meisn. → Koenigia polystachya

Polygonum species that have been reclassified as Persicaria

 * Polygonum alatum → Persicaria nepalensis
 * Polygonum amphibium – amphibious bistort, longroot smartweed, water smartweed → Persicaria amphibia
 * Polygonum capitatum – pinkhead smartweed → Persicaria capitata
 * Polygonum chinense L. → Persicaria chinensis
 * Polygonum coccineum Muhl. ex Willd. → Persicaria amphibia
 * Polygonum filiforme Thunb. → Persicaria filiformis
 * Polygonum hydropiper – water-pepper → Persicaria hydropiper
 * Polygonum hydropiperoides Michx. – swamp smartweed → Persicaria hydropiperoides
 * Polygonum lapathifolium – pale persicaria or nodding smartweed → Persicaria lapathifolia
 * Polygonum longisetum → Persicaria longiseta
 * Polygonum minus – small water-pepper → Persicaria minor
 * Polygonum mite Schrank – tasteless water-pepper → Persicaria mitis (Schrank) Assenov
 * Polygonum nepalense → Persicaria nepalensis
 * Polygonum odoratum Lour. – Vietnamese coriander → Persicaria odorata
 * Polygonum orientale → Persicaria orientalis
 * Polygonum pensylvanicum – Pennsylvania smartweed or pink knotweed or pinkweed → Persicaria pensylvanica
 * Polygonum perfoliata – Asiatic Tearthumb → Persicaria perfoliata
 * Polygonum persicaria – redshank or persicaria or lady's thumb → Persicaria maculosa
 * Polygonum praetermissum → Persicaria praetermissa
 * Polygonum punctatum Elliott – dotted smartweed → Persicaria punctata
 * Polygonum runcinatum → Persicaria runcinata
 * Polygonum sagittatum – arrowleaf tearthumb, American tear-thumb or scratchgrass → Persicaria sagittata
 * Polygonum tinctorium → Persicaria tinctoria
 * Polygonum virginianum L. → Persicaria virginiana

Polygonum species that have been reclassified as Reynoutria

 * Polygonum multiflorum Thunb. → Reynoutria multiflora
 * Polygonum cuspidatum Siebold & Zucc. – Japanese knotweed → Reynoutria japonica
 * Polygonum sachalinense F.Schmidt – giant knotweed → Reynoutria sachalinensis

Unresolved species

 * Polygonum vaccinifolium Wall. is an unresolved species name. Persicaria vaccinifolia may be a synonym.

Uses
Several species can be eaten cooked, for example during famines. The species Polygonum cognatum, known locally as "madimak", is regularly consumed in central parts of Turkey.

References in literature
In The Man Who Laughs Victor Hugo wrote of the Comprachicos (child-buyers) who created artificial dwarfs, formed "by anointing babies' spines with the grease of bats, moles and dormice" and using drugs such as "dwarf elder, knotgrass, and daisy juice". The idea of such use was also known to Shakespeare, as Beatrice K. Otto pointed out, quoting A Midsummer Night's Dream:

Get you gone, dwarf; You minimus, of hindering knot-grass made;