Polygonum

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(Redirected from Knotgrass)

{{Taxobox | color = lightgreen | name = Polygonum | image = PolygonumPersicara-flower-sm.jpg | image_width = 240px | image_caption = Polygonum persicara flowerhead | regnum = Plantae | divisio = Magnoliophyta | classis = Magnoliopsida | ordo = Caryophyllales | familia = Polygonaceae | genus = Polygonum | genus_authority = L. | subdivision_ranks = Species | subdivision = Between 150-300 species; see text }}

Polygonum is a genus in the buckwheat family Polygonaceae. The name is probably derived from the Greek poly, "many" and gonu, "knot". There is another theory which states that the second part of the name is derived from Greek gonos, "children". Common names include knotweed, knotgrass, bistort and several others.

Image:Japaneseknotweedfoliage.jpg 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.

Many knotweed species, particularly Japanese, Giant and Himalayan knotweed are considered noxious, invasive pests. Like many such weeds, Japanese knotweed was introduced from Japan first into the U.K., then into North America in the 19th century as an ornamental plant. Recently, the Japanese knotweed and others have been used to exploit their high concentrations of trans-resveratrol in the plants' stalks. Previously associated with and identified mainly in the skins of red grapes, resveratrol is currently under study in a number of research projects investigating its reputedly powerful antiaging properties.

Some knotweeds grow extremely quickly during the spring; Giant knotweed can reach 4.5 m by summer, Japanese knotweed 3 m, and 'dwarf' Himalayan knotweed 1.5-2 m. In Japan, Japanese knotweed is known as itadori, or 'strong plant'. Some species can spread rapidly from an extensive network of rhizomes (roots that can sprout) spreading from 7-20 m from the parent plant and at least 2 m deep. Root and stem fragments as small as 1 cm can form new plant colonies. Floods and high water events wash whole or partial plants into rivers and creeks, dispersing pieces of knotweed throughout the flooded area and banks, which give rise to new plants. As with other invasive species of plants, freshly disturbed soil allows the rapidly growing young knotweed plants to outgrow other plants and take over the area, suppressing other species. Cutting, mowing, digging and some herbicide treatments, especially in early to mid growing season, fail to curb knotweed growth and in fact often stimulate the production of shoots from latent buds dispersed on the root crown or rhizomes.

Polygonum cuspidatum are being used in treating cancer.

Polygonum species are used as food plants by the larvae of some Lepidoptera species - see list of Lepidoptera which feed on Polygonum.

Between 150-300 species are recognised depending on the circumscription of the genus; some botanists divide the genus up into several smaller genera. Selected species include:

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External links

Nonspecific Biological Immune Response ]da:Pileurt de:Knöteriche eo:Poligono fr:Renouée ko:싱아 nl:Duizendknoop pl:Rdest zh:蓼

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