Persicaria lapathifolia (L.) Delarbre, Fl. Auvergne ed. 2: 519 1800. (syn: Dioctis maculatum Raf.; Dioctis vernum Raf.; Discolenta lapathifolia Raf.; Discolenta scabra Raf.; Persicaria attenuata subsp. pulchra (Blume) K.L. Wilson; Persicaria hypanica (Klokov) Tzvelev; Persicaria lapathifolia (L.) Gray …………………..; Persicaria linicola (Sutulov) Nenukow; Persicaria oneillii Brenckle; Persicaria saporoviensis (Klokov) Tzvelev; Persicaria scabra (Moench) Moldenke .; Persicaria tomentosa (Schrank) E.P.Bicknell; Peutalis nodosa (Pers.) Raf.; Polygonum andrzejowskianum Klokov; Polygonum brittingeri Opiz; Polygonum ferrugineum var. patagonicum (Speg.) Macloskie; Polygonum glandulosum Kit.; Polygonum hypanicum Klokov; Polygonum incanum F.W.Schmidt; Polygonum incarnatum Elliott; Polygonum lapathifolium L. ……….; Polygonum linicola Sutulov; Polygonum mariae V.N. Vassil.; Polygonum nodosum Pers. .; Polygonum pallidum With.; Polygonum paniculatum Andrz. [Illegitimate]; Polygonum pensylvanicum subsp. oneilii (Brenckle) Hultén; Polygonum persicaria var. incanum (F.W. Schmidt) Meisn.; Polygonum persicaria var. incanum Roth; Polygonum persicaria var. vernicosum Cham. & Schltdl.; Polygonum saporoviense Klokov; Polygonum scabrum Moench; Polygonum spectabile var. patagonica Speg.; Polygonum tomentosum Schrank; Polygonum utriculatum Remy);
Subarctic & Temp. Northern Hemisphere to W. & Central Malesia, N. Africa to Ethiopia: Afghanistan, Alabama, Alaska, Albania, Alberta, Algeria, Altay, Amur, Arizona, Arkansas, Ascension, Assam, Austria, Azores, Baleares, Baltic States, Bangladesh, Belarus, Belgium, Bulgaria, Buryatiya, California, Central European Rus, China North-Central, China South-Central, China Southeast, Chita, Colorado, Connecticut, Corse, Cyprus, Czechoslovakia, Delaware, Denmark, District of Columbia, East Aegean Is., East European Russia, East Himalaya, Egypt, Ethiopia, Finland, Florida, France, Føroyar, Georgia, Germany, Great Britain, Greece, Greenland, Hainan, Hungary, Idaho, Illinois, India, Indiana, Inner Mongolia, Iowa, Iran, Iraq, Ireland, Irkutsk, Italy, Jawa, Kamchatka, Kansas, Kazakhstan, Kentucky, Khabarovsk, Kirgizstan, Korea, Krasnoyarsk, Kriti, Krym, Kuril Is., Labrador, Lebanon-Syria, Louisiana, Madeira, Magadan, Maine, Manchuria, Manitoba, Maryland, Massachusetts, Mexico Central, Mexico Southwest, Michigan, Minnesota, Mississippi, Missouri, Mongolia, Montana, Morocco, Myanmar, Nebraska, Nepal, Netherlands, Nevada, New Brunswick, New Guinea, New Hampshire, New Jersey, New Mexico, New York, Newfoundland, North Carolina, North Caucasus, North Dakota, North European Russi, Northwest European R, Northwest Territorie, Norway, Ohio, Oklahoma, Ontario, Oregon, Pakistan, Palestine, Pennsylvania, Philippines, Poland, Portugal, Primorye, Prince Edward I., Qinghai, Québec, Rhode I., Romania, Sakhalin, Sardegna, Saskatchewan, Sicilia, South Carolina, South Dakota, South European Russi, Spain, Sumatera, Sweden, Switzerland, Tadzhikistan, Taiwan, Tennessee, Texas, Thailand, Tibet, Transcaucasus, Tunisia, Turkey, Turkey-in-Europe, Turkmenistan, Tuva, Ukraine, Utah, Uzbekistan, Vermont, Vietnam, Virginia, Washington, West Himalaya, West Siberia, West Virginia, Wisconsin, Wyoming, Xinjiang, Yakutskiya, Yemen, Yugoslavia, Yukon as per POWO;
Common name: Pale Knotweed, Pale Persicaria, Pale smartweed, Curlytop knotweed, Willow weed • Manipuri: চাওখোঙ মানবা Chaokhong-manba
Pale persicaria (Persicaria lapathifolia (L.) Delarbre, syn. Polygonum lapathifolium L.) is a plant of the family Polygonaceae. It is closely related to Redshank and as such is considered a weed in Britain and Europe. Other common names for the plant include pale smartweed, curlytop knotweed, and willow weed.
The species is a species complex made up of a great many varying forms, sometimes considered varieties. The environment also has a strong influence on the morphology of an individual plant.
Pale persicaria is an annual herb with erect reddish stems with swollen joints, growing to a height of 20 to 80 cm (8 to 31 in). The leaves are alternate with short stalks, often densely hairy underneath. The leaf blades often have a dark-coloured blotch in the centre and are lanceolate or narrowly elliptical and have entire margins. Each leaf base has stipules which are fused into a stem-enclosing sheath that is loose and fringed with few if any hairs at the upper end. The inflorescence is a dense spike, often nodding. The perianth of each tiny pink flower consists of four or five lobes, fused near the base. There are six stamens, two partially fused carpels and two styles. The fruit is a rounded, flattened nut. This plant flowers from July to September.
Pale persicaria is found in many parts of both the Old World and New World. There are many varieties and sub-species and the plant is morphologically variable. 
It is found growing on the sea shore and in disturbed ground such as arable land, gardens, waste ground, rubbish tips and road verges.
(From Wikipedia on 8.1.14)
Persicaria lapathifolia from Kashmir : Attachments (3). 2 posts by 2 authors.
Persicaria lapathifolia (L) Delarbre (syn: Polygonum lapathifolium L.) from Kashmir, growing in wet places, along drains and ditches.
Photographed from Botanical Garden near Cheshmashahi on June 26, 2010
Common Names: Pale persicaria, Pale smartweed
Used against cancer. Herb is suspected of causing dermatitis and death in cattle.
Polygonaceae Fortnight: Plant of Central Java 13 : 4 posts by 3 authors. Attachments (1).
Could you help me to id our Polygonum please.
More likely Persicaria lapathifolia
Agree with … ID.
Leaves with red blotches, eciliate ochrea and other leaf characters are pointing towards P. lapathifolia.
Polygonaceae Fortnight: Persicaria lapathifolia from Kashmir-GSMAY36: 2 posts by 2 authors. Attachments (3).
Persicaria lapathifolia (L.) Delarbre
syn: Polygonum lapathifolium L.
Another characteristic species of moist places having dark curved patches on leaves like P. capitata but with linear-lanceolate leaves and slender inflorescence.
Common along drains, ditches and stream banks in Kashmir. Photographed from Srinagar.
Yes! This looks like a typical P. lapathifolia to me too. Thanks for sharing the beautiful photographs.
SK784 09 OCT-2017:ID : 3 posts by 2 authors. Attachments (6)
Location : Tatopani, Pokhara, Nepal
Date : 8 April 2017
I think Persicaria lapathifolia (L.) Delarbre
Persacaria Id from Bangladesh_SM_1424 : 4 posts by 3 authors. Attachments (1)
Habitat: Road side
I can see a purple blotch on the leaves. Most likely Persicaria lapathifolia (L.) Delabre
Polygonaceae for ID : 5 posts by 3 authors. Attachments (2).
It is Persicaria barbata (L.) H.Hara (= Polygonum barbatum L.); which is frequently available near roadside canals.
the plant uploaded is a variety of Persicaria lapathifolia as P. barbata has long cilia at ochrea being diagnostic feature