Persicaria lapathifolia
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Order:	Caryophyllales
Family:	Polygonaceae
Genus:	Persicaria
Species:	P. lapathifolia
Binomial name
Persicaria lapathifolia (L.) Delarbre 1800
Synonyms[1]
Synonymy Polygonum lapathifolium L. 1753 Persicaria lapathifolia (L.) S.F.Gray 1821 Dioctis maculatum Raf. Dioctis vernum Raf. Discolenta lapathifolia Raf. Discolenta scabra Raf. Persicaria brittingeri Opiz Persicaria hypanica (Klokov) Tzvelev Persicaria linicola (Sutulov) Nenukow Persicaria oneillii Brenckle Persicaria saporoviensis (Klokov) Tzvelev Persicaria scabra (Moench) Moldenke Peutalis incana Raf. Peutalis nodosa (Pers.) Raf. Peutalis scabra Raf. Pogalis tomentosa Raf. Polygonum andrzejowskianum Klokov Polygonum brittingeri Opiz Polygonum hypanicum Klokov Polygonum incanum F.W.Schmidt Polygonum incarnatum Elliott Polygonum linicola Sutulov Polygonum nodosum Pers. Polygonum pallidum With. Polygonum paniculatum Andrz. 1862 not L. 1759 Polygonum saporoviense Klokov Polygonum scabrum Moench Polygonum tomentosum Schrank Polygonum utriculatum Remy plus many more names at level of subspecies, variety, or form

Wikispecies has information related to Persicaria lapathifolia.

Persicaria lapathifolia (syn. Polygonum lapathifolium), known as pale persicaria,^[2] is a plant of the family Polygonaceae. It is considered to be native throughout most of the world, from arctic to tropical realms, except South America and Southern Africa.^[3] It is closely related to Persicaria maculosa 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. It 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.

Persicaria lapathifolia 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 in northern temperate regions.^[4][5]

Persicaria lapathifolia is found in many parts of both the Old World and New World.^{[5][6][7][8][9]} Many varietal and sub-specific names have been coined, as the plant is morphologically variable. The species is found growing on the sea shore and in disturbed ground such as arable land, gardens, waste ground, rubbish tips and road verges.^[4]

• Jepson eFlora
• photo of herbarium specimen at Missouri Botanical Garden, collected in Missouri in 1890
• Calphotos Photo gallery, University of California