knotgrass n : low-growing weedy grass with spikelets along the leaf stems [syn: Paspalum distichum]

Polygonum is a genus in the buckwheat family Polygonaceae. The name may be derived from the Greek poly, "many" and gonu, "knee" in reference to the swollen jointed stem nodes. There is another theory which states that the second part of the name is derived from Greek gonos, "children" or gone, "seed". There have been various opinions about how broadly the genus should be defined. Buckwheat for example has sometimes been included in the genus.

The genus primarily grows in northern temperate regions. They vary widely from prostrate herbaceous annual plants under 5 cm high, others erect herbaceous perennial plants growing to 3–4 m tall, and yet others perennial woody vines growing to 20–30 m high in trees; several are also aquatic, growing as floating plants in ponds. The smooth-edged leaves vary greatly in shape between species, and can be narrow lanceolate, oval, broad triangular, heart shaped or arrowhead shaped; they range from 1–30 cm long. The stems are often reddish or red-speckled. The flowers are small, pink, white, or greenish, forming in summer in dense clusters from the leaf joints or stem apices.

Polygonum species are used as food plants by the larvae of some Lepidoptera species - see list of Lepidoptera that feed on Polygonum, a number are considered weedy, especially in moisture retentive soils in the USA.

Distribution and Uses

At least one species has been eaten during times of famine.

Species

Between 65–300 species are recognised depending on the circumscription of the genus; some botanists divide the genus up into several smaller genera, including Fagopyrum, Fallopia and Persicaria.

The genus Polygonella has a number of morphological similarities with Polygonum and some authors have included Polygonella in Polygonum.

Selected species include:

• Polygonum achoreum
• Polygonum acuminata
• Polygonum acuminatum - tapertip smartweed
• Polygonum arenarium
• Polygonum arenastrum – small-leaved knotgrass
• Polygonum argyrocoleon
• Polygonum arifolium
• Polygonum aviculare – common knotgrass
• Polygonum bellardii
• Polygonum bidwelliae
• Polygonum bistortoides
• Polygonum bolanderi
• Polygonum boreale
• Polygonum brasiliensis
• Polygonum bungeanum - Bunge's smartweed
• Polygonum buxiforme
• Polygonum caespitosum
• Polygonum californicum – California knotweed
• Polygonum careyi - Carey's smartweed
• Polygonum cascadense
• Polygonum caurianum
• Polygonum chinense
• Polygonum coccineum
• Polygonum cognatum – Indian knotgrass
• Polygonum davisiae
• Polygonum densiflorum
• Polygonum dibotrys
• Polygonum douglasii – Douglas' knotweed
• Polygonum erectum
• Polygonum flaccidum – (Meissn.)
• Polygonum foliosum
• Polygonum forrestii
• Polygonum fowleri
• Polygonum franktonii
• Polygonum glaucum
• Polygonum griffithii
• Polygonum herniarioides
• Polygonum heterosepalum – dwarf desert knotweed
• Polygonum hickmanii
• Polygonum hirsutum
• Polygonum hongkongensis
• Polygonum hudsonianum
• Polygonum hydropiperoides - swamp smartweed
• Polygonum lacerum
• Polygonum lanigerum
• Polygonum marinense
• Polygonum maritimum – sea knotgrass
• Polygonum meisneranum
• Polygonum meisnerianum
• Polygonum minimum – broadleaf knotweed
• Polygonum multiflorum
• Polygonum newberryi - Newberry knotweed
• Polygonum oxyspermum – Ray's knotgrass
• Polygonum paronychia
• Polygonum paronychioides
• Polygonum parryi
• Polygonum patulum - Bellard's smartweed
• Polygonum perfoliatum – mile-a-minute weed
• Polygonum phytolaccifolium
• Polygonum plebeium
• Polygonum polycnemoides
• Polygonum polycnenoides
• Polygonum polygaloides
• Polygonum punctatum - dotted smartweed
• Polygonum raii = Polygonum oxyspermum
• Polygonum ramosissimum
• Polygonum robustius - stout smartweed
• Polygonum rurivagum
• Polygonum salicifolium
• Polygonum scoparium
• Polygonum segetum - field smartweed
• Polygonum setaceum - bog smartweed
• Polygonum shastense
• Polygonum striatulum
• Polygonum tenue

Reclassified as Fagopyrum

• Polygonum fagopyrum (Fagopyrum esculentum) – buckwheat

Reclassified as Fallopia

• Polygonum aubertii = Polygonum baldschuanicum
• Polygonum baldschuanicum (Fallopia baldschuanica) (Fallopia aubertii, Bilderdykia aubertii, Bilderdykia balschuanicum) – Russian vine
• Polygonum cilinode (Fallopia cilinodis, Bilderdykia cilinodis) – fringed black bindweed
• Polygonum convolvulus (Fallopia convolvulus) – Black Bindweed, wild buckwheat
• Polygonum cuspidatum = Polygonum japonicum - Japanese knotweed
• Polygonum dumetorum (Fallopia dumetorum) – copse bindweed
• Polygonum japonicum (Fallopia japonica, Reynoutria japonica) – Japanese knotweed
• Polygonum multiflorum (Fallopia multiflora)
• Polygonum sachalinense (Fallopia sachalinensis, Reynoutria sachalinensis) – giant knotweed
• Polygonum scandens (Fallopia scandens)

Reclassified as Persicaria

• Polygonum affine (Persicaria affinis)
• Polygonum alatum (Persicaria alata)
• Polygonum alpinum – alpine knotweed (Persicaria alpina)
• Polygonum amphibium – amphibious bistort, longroot smartweed, water smartweed, (Persicaria amphibia)
• Polygonum amplexicaule (Persicaria amplexicaulis)
• Polygonum bistorta – bistort (Persicaria bistorta)
• Polygonum campanulatum – lesser knotweed, bellflower smartweed, (Persicaria campanulata) (Reynoutria campanulatum)
• Polygonum capitatum - pinkhead smartweed, (Persicaria capitata)
• Polygonum emodi (Persicaria emodi)
• Polygonum filiforme (Persicaria virginiana)
• Polygonum hydropiper – water-pepper (Persicaria hydropiper)
• Polygonum lapathifolium – pale persicaria or nodding smartweed (Persicaria lapathifolia)
• Polygonum longisetum (Persicaria longiseta)
• Polygonum macrophyllum (Persicaria macrophylla)
• Polygonum milletii (Persicaria milletii)
• Polygonum minus – small water-pepper (Persicaria minor)
• Polygonum mite – tasteless water-pepper (Persicaria mitis, Persicaria laxiflora)
• Polygonum molle (Persicaria mollis)
• Polygonum nepalense (Persicaria nepalensis)
• Polygonum odoratum – Vietnamese coriander (Persicaria odorata)
• Polygonum orientale (Persicaria orientalis)
• Polygonum pensylvanicum – Pennsylvania smartweed or pink knotweed or pinkweed (Persicaria pensylvanica)
• Polygonum persicaria – redshank or persicaria or lady's thumb (Persicaria maculosa)
• Polygonum polystachyum = Polygonum wallichii
• Polygonum runciforme (Persicaria runcinata)
• Polygonum sagittatum – arrowleaf tearthumb, American tear-thumb or scratchgrass (Persicaria sagittata)
• Polygonum tenuicaule (Persicaria tenuicaulis)
• Polygonum tinctorium (Persicaria tinctoria)
• Polygonum vaccinifolium (Persicaria vaccinifolia)
• Polygonum virginianum (Persicaria virginiana)
• Polygonum viviparum – alpine bistort (Persicaria vivipara)
• Polygonum wallichii – Himalayan knotweed (Persicaria wallichii)
• Polygonum weyrichii (Persicaria weyrichii)

References/External links

• Website of the Natural History Museum, London
• Plant Finder section of the Royal Horticultural Society's website
• Flora of Northern Ireland

References