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Persicaria lapathifolia; photograph (c) Josep Gesti, some rights reserved (CC BY-SA) CC BY-SA(c) Josep Gesti, some rights reserved (CC BY-SA) · observed growing wild · 2026-09-26

Persicaria lapathifolia (L.) Delarbre

Curlytop knotweed; Pale smartweed; Dockweed Smartweed; Pale Persicaria

Polygonaceae · Denmark, Finland +180

Cited as Kew's World Checklist cites it, Persicaria lapathifolia (L.) Delarbre: GBIF's backbone key for this page carries the name with another author, (L.) Gray.

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Persicaria lapathifolia, photograph (c) Sandy Wolkenberg, some rights reserved (CC BY)Persicaria lapathifolia, photograph (c) Sandy Wolkenberg, some rights reserved (CC BY)Persicaria lapathifolia, photograph (c) Sandy Wolkenberg, some rights reserved (CC BY)Persicaria lapathifolia, photograph (c) Trevor Van Loon, some rights reserved (CC BY)Persicaria lapathifolia, photograph (c) Josep Gesti, some rights reserved (CC BY-SA)Persicaria lapathifolia, photograph (c) Alex Abair, some rights reserved (CC BY) 74 photographs ›
Habitat figures
Cold floor (1 night in 100)
-11.2°C
Record low -22.6 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
22°C
Jul at the habitat CHELSA
Rain a year (median across the range)
794mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
4–36DLI
Lowest to highest month (DLI) CHELSA
The year in your months, northern hemisphere
  1. Jan
  2. Feb
  3. Mar
  4. Apr
  5. May
  6. Jun
  7. Jul
  8. Aug
  9. Sep
  10. Oct
  11. Nov
  12. Dec
Rain spread: 70% of the median year's rain takes 8 months, so no short rainy season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Summary

Persicaria lapathifolia (syn. Polygonum lapathifolium), known as pale persicaria, 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. 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. More on Wikipedia ›

Quoted from Wikipedia, "Persicaria lapathifolia", CC BY-SA 4.0.

Cultivation

Seasons

The rain rule reads no short rainy season: 70% of the median year's rain (576 mm of 787 mm) takes 8 months, June to January. Mean temperature moves 16.7 °C between the warmest and coldest month. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: December to July.

Rain

787 mm in the median year at the habitat, 576 mm of it June to January. Wettest months (2 at 78 mm), driest month April at 46 mm. Across the grid cells of the range the year's total runs 591 mm to 1,303 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 794 mm, is the year's rain at the top of the page; the 787 mm here is the median year's, the twelve monthly medians added, which the rain rule reads. Habitat calendar, northern hemisphere; median year across the grid cells of the range, CHELSA.

Light

Open sky over the habitat: 4 to 36 mol/m²/day across the year (daily light integral, median year across the grid cells of the range, CHELSA; the lowest 10th-percentile month across the cells is 1, the highest 90th-percentile month 43).

Warmth and air
Temperature

Coldest: the 1st-percentile night over 44 years at a typical spot in the range is -11.2 °C, the absolute minimum -22.6 °C, 3,788 frost nights in 44 years, 86.1 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 36.3 °C. Monthly means: the coldest month's mean nightly low -1.6 °C in January (across the grid cells of the range -9.2 °C to 8.7 °C), the warmest month's mean daily high 21.5 °C in July (median year across the grid cells of the range, CHELSA). Cold floor: -11.2 °C, which is the 1st-percentile night over 44 years at a typical spot in the range (NASA POWER).

Humidity

Relative humidity at the habitat: 58 to 68% across the year (monthly means, median year across the grid cells of the range, CHELSA). A figure about the air, saying nothing about how the plant takes water.

How this section is made

Each card states this species' habitat figures with their sources, and what two fixed rules read from them; nothing here says what the plant does, wants or tolerates. The rules · the terms.

Seasons. Read from the median year of CHELSA monthly rainfall and mean temperature across the grid cells of the range: the rain rule takes the smallest set of months carrying 70% of the rain and calls it winter when its mean is more than half a degree below the year's, summer when more than that above, and neither in between; the temperature rule, used only under 120 mm, names the cooler six months when they are at least a degree cooler than the other six. Months are shifted for the other hemisphere only where the temperature curve moves 4 °C or more and the habitat lies 10° or more from the equator. A reading of the curves, not an observation of the plant.

Rain. CHELSA monthly precipitation, median year across the grid cells of the range. The rain that falls where the species is recorded; nothing about how the plant takes water.

Light. CHELSA shortwave radiation at each envelope cell, a daily-mean flux taken to a daily total and converted at 2.07 mol of PAR per MJ. The sky over the habitat, measured; what reaches a plant under a rock, a shrub or a shade cloth is not.

Temperature. NASA POWER daily minima and maxima over 44 years at a typical spot in the range, lapse-corrected -189 m to its elevation; CHELSA monthly means, median year across the grid cells of the range. The cold floor is the 1st-percentile night named in its sentence. Not a measured survival limit for any plant in a pot.

Humidity. CHELSA relative humidity, median year across the grid cells of the range.

Climate across the habitat

Habitat months, northern hemisphere

Habitat climate of Persicaria lapathifolia through the yearWarmest month July, mean daily high 22 °C; coldest month January, mean nightly low -1.6 °C; 787 mm of rain in the median year (the twelve monthly medians added). Medians across the range, from CHELSA; the extremes at the edge from NASA POWER. Habitat months, northern hemisphere.-30°-20°-10°0°10°20°30°40°frost36.3° 99th-percentile day, NASA POWER-22.6° lowest night in 44 years, NASA POWER°C · day and nightcold quarter0255075100125mm rainDLI 4–36RH 58–68%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 1154 habitat cells, CHELSA cold quarter: the three months around the coldest month's mean nightly low extremes over 44 years at a typical spot in the range, from NASA POWER, marked at the edge, in no month DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C3 / -4–185 / -4–199 / 0–2112 / 7–2316 / 13–2619 / 16–2922 / 18–3120 / 18–3117 / 14–2913 / 8–258 / 2–214 / -2–18
Night °C-2 / -9–9-1 / -9–101 / -6–114 / 0–128 / 5–1511 / 9–2014 / 12–2214 / 11–2210 / 8–197 / 3–143 / -2–110 / -7–10
Rain mm61 / 34–9751 / 31–8855 / 34–10046 / 32–9559 / 39–12372 / 49–12578 / 48–12278 / 50–12271 / 49–11577 / 40–11473 / 45–10766 / 42–104
DLI5 / 2–2010 / 6–2517 / 14–3327 / 24–3734 / 31–4036 / 32–4234 / 31–4328 / 25–4019 / 16–3311 / 7–296 / 3–234 / 1–19
RH %67 / 57–7265 / 57–7063 / 56–6559 / 55–6258 / 56–6259 / 57–6360 / 57–6361 / 56–6363 / 57–6465 / 56–6767 / 57–7068 / 57–72
How this section is made
Each figure is the median across the 1154 grid cells on land that hold in-range records (1513 records in those cells; 27 more cells hold records but no land by the elevation layer, so those records sit at sea and the cells are left out), with the 10th–90th percentile span across those cells after the slash where it differs. A dash is a month one or more of those cells has no figure for in the grid (a variable CHELSA does not carry there), so no median is taken rather than one over fewer cells. Extremes and elevation were read at a typical spot in the range, cell 1055:2004 (37.225, -79.775). Over 44 years there: absolute minimum -22.6 °C, 1st-percentile night -11.2 °C, 99th-percentile day 36.3 °C. Normals: CHELSA V2.1 1981–2010 climatology, 0.05° cells (each the mean of ~36 1 km pixels). Across the range: median and 10th–90th percentile of each month across the 1154 distinct grid cells holding 1513 of the 1541 in-range records (27 further cells with records at sea, by the elevation layer, left out); extremes and elevation at the typical cell 1055:2004 (its coldest month's mean nightly low nearest the median across cells); its position is the cell centre. Extremes: NASA POWER (MERRA-2) daily 1981–2024, cell 37.00_-80.000, lapse-corrected -189 m at 6.5 °C/km. Elevation: ETOPO 2022, 282 m (cell mean).

Natural habitat

Native range as published by WCVP; the marker is where the records are densest and decides nothing: the climate was read across the cells of the in-range records placed well enough to read one, not at the marker.
Openly licensed records inside the range, framed on where they fall.
NativeDenmark, Finland, Føroyar, Great Britain, Ireland, Norway, Sweden, Austria, Belgium, Czechoslovakia, Germany, Hungary, Netherlands, Poland, Switzerland, Baleares, Corse, France, Portugal, Sardegna, Spain, Albania, Bulgaria, Greece, Italy, Kriti, Romania, Sicilia, Turkey-in-Europe, Yugoslavia, Belarus, Baltic States, Krym, Central European Russia, East European Russia, North European Russia, South European Russia, Northwest European Russia, Ukraine, Algeria, Egypt, Morocco, Tunisia, Azores, Madeira, Benin, The Gambia, Guinea, Mauritania, Central African Republic, Ethiopia, Ascension, Altay, Buryatiya, Chita, Irkutsk, Krasnoyarsk, Tuva, West Siberia, Yakutskiya, Amur, Kamchatka, Khabarovsk, Kuril Is., Magadan, Primorye, Sakhalin, Kazakhstan, Kirgizistan, Turkmenistan, Tadzhikistan, Uzbekistan, North Caucasus, Transcaucasus, Afghanistan, Cyprus, East Aegean Is., Iran, Iraq, Lebanon-Syria, Palestine, Turkey, Yemen, China South-Central, Hainan, Inner Mongolia, Manchuria, China North-Central, Qinghai, China Southeast, Tibet, Xinjiang, Mongolia, Japan, Korea, Nansei-shoto, Taiwan, Assam, Bangladesh, East Himalaya, India, Nepal, Pakistan, West Himalaya, Laos, Myanmar, Thailand, Vietnam, Jawa, Philippines, Sumatera, New Guinea, New South Wales, Northern Territory, Queensland, South Australia, Victoria, Western Australia, Alaska, Greenland, Northwest Territories, Yukon, Alberta, Manitoba, Saskatchewan, Labrador, New Brunswick, Newfoundland, Ontario, Prince Edward I., Québec, Colorado, Idaho, Montana, Oregon, Washington, Wyoming, Illinois, Iowa, Kansas, Minnesota, Missouri, North Dakota, Nebraska, Oklahoma, South Dakota, Wisconsin, Connecticut, Indiana, Maine, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode I., Vermont, West Virginia, Arizona, California, Nevada, Utah, New Mexico, Texas, Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, District of Columbia, Mexico Central, Mexico Southwest · introduced: Malawi, Mozambique, Zambia, Zimbabwe, Botswana, Free State, Tasmania, New Zealand North, Bolivia, Argentina Northeast, Argentina South, Argentina Northwest, Chile Central, Chile South, Juan Fernández Is., Paraguay, Uruguay · regions are the level-3 units of the World Geographical Scheme for Recording Plant Distributions, as Kew's World Checklist records ranges, some under historical names such as Yugoslavia or Czechoslovakia (how).
Map marker49.556, 6.307 · in the densest population, 530 records (33% of those in range)
Kew's description“annual” · “temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 1583 georeferenced records inside the native range; the climate across the range on the 1513 of them in the land cells it reads, of 1541 placed to within 10 km; the map shows only the 881 openly licensed ones, which alone would put the marker 720 km away. 58 records outside the WCVP native range not used. 42 in-range records are placed to worse than 10 km, or with no stated accuracy (admitted only as a person's observation to three decimals), and stay on the map but off the climate.
Other GBIF keysRecords also from GBIF's key 7820611 (Persicaria lapathifolia (L.) Delarbre): Kew's file holds it as Persicaria lapathifolia (L.) Delarbre (accepted); 900 records, from GBIF's search API on the day of the build.Records also from GBIF's key 10972738 (Persicaria lapathifolia (L.) H.Gross, 1913): Kew's file holds it as Persicaria lapathifolia (L.) Delarbre (accepted); 0 records, from GBIF's search API on the day of the build.
How this section is made
The map marker: the openly licensed record nearest the middle of the densest 1° population inside the densest 4° block of the 1583 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Persicaria lapathifolia, photograph 1did not loadPersicaria lapathifolia, photograph 2did not loadPersicaria lapathifolia, photograph 3did not loadPersicaria lapathifolia, photograph 4did not loadPersicaria lapathifolia, photograph 5did not loadPersicaria lapathifolia, photograph 6did not load

Photographs: (c) Sandy Wolkenberg, some rights reserved (CC BY) (3); (c) Trevor Van Loon, some rights reserved (CC BY); (c) Josep Gesti, some rights reserved (CC BY-SA); (c) Alex Abair, some rights reserved (CC BY).

Similar habitat climate The 6 nearest by mean daily high, mean nightly low and rain, month by month. How.

Eleocharis acicularis Eleocharis acicularis Needle spike-rush Photo: CC BY, Jason GrantOdontites vulgaris Odontites vulgaris Red odontites Photo: CC0, author not statedPolygonum arenastrum Polygonum arenastrum Equal-leaved Knotgrass Photo: CC BY, Bernhard HildebrandJuncus compressus Juncus compressus Round-fruited rush Photo: CC BY, Johnathan CampbellVeronica agrestis Veronica agrestis Green field-speedwell Photo: CC0, author not statedLimosella aquatica Limosella aquatica Mudwort Photo: CC0, author not stated

Other Persicaria 42 in the reference

Persicaria acuminata Persicaria acuminata Tapertip Smartweed Photo: CC BY, Seba FernándezPersicaria amphibia Persicaria amphibia Amphibious bistort Photo: CC BY, Sandy WolkenbergPersicaria arifolia Persicaria arifolia Halberd-leaved tearthumb Photo: CC BY-SA, V. Ross JohnsonPersicaria attenuata Persicaria attenuata Watersmart Weed Photo: CC0, author not statedPersicaria barbata Persicaria barbata Bearded knotweed Photo: CC BY, chiuluanPersicaria biconvexa Persicaria biconvexa Polygonaceae Photo: CC0, 葉子Persicaria bicornis Persicaria bicornis Pink smartweed Photo: CC0, author not statedPersicaria capitata Persicaria capitata Pinkhead smartweed Photo: CC0, author not statedPersicaria chinensis Persicaria chinensis Chinese knotweed Photo: CC BY, Ben CostamagnaPersicaria decipiens Persicaria decipiens Slender knotweed Photo: CC BY, Duarte FradePersicaria dichotoma Persicaria dichotoma Polygonaceae Photo: CC BY, 如此甚好Persicaria extremiorientalis Persicaria extremiorientalis Far-Eastern smartweed Photo: CC BY, Heather Mazzaccaro all 43 ›

Names & registers

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Polygonaceae
Described by
(L.) Delarbre
Native to
Denmark, Finland, Føroyar +179
Wild records
1583 in range · 881 open

Every figure here is derived from public data by a stated rule and names its source; nothing about this species is written for its page by a person or by AI, apart from the marked, credited quotations. How →

Where this page came from built 2026-10-22
GBIF species record gbif.species answeredasked 2026-10-22GBIF's key 2889262 is Persicaria lapathifolia (L.) Gray; the page links Kew's Persicaria lapathifolia (L.) Delarbre, and the name is cited as Kew cites it
GBIF synonyms gbif.synonyms answeredasked 2026-10-22
GBIF common names gbif.vernacular answeredasked 2026-10-22names fetched 2026-10-22
WCVP native range wcvp.distribution answeredas of 2026-06-04
GBIF occurrence records gbif.occurrences answeredasked 2026-10-22GBIF occurrence search API; 900 records of GBIF's key 7820611, Persicaria lapathifolia (L.) Delarbre (Kew's file holds it as Persicaria lapathifolia (L.) Delarbre (accepted)): GBIF occurrence search API; 0 records of GBIF's key 10972738, Persicaria lapathifolia (L.) H.Gross, 1913 (Kew's file holds it as Persicaria lapathifolia (L.) Delarbre (accepted)): GBIF occurrence search API; 31 records within 1 km of a botanic garden, herbarium or zoo left out (15 at a botanic garden or arboretum, 2 at a herbarium, 14 at a zoo; Wikidata's list)
Habitat climate climate answeredasked 2026-10-22
Daily extremes (NASA POWER) climate.extremes answeredasked 2026-10-22NASA POWER (MERRA-2) daily 1981–2024, cell 37.00_-80.000, lapse-corrected -189 m at 6.5 °C/km
Wikidata wikidata answeredasked 2026-10-22
Wikipedia wikipedia answeredasked 2026-10-22
iNaturalist photographs, wild inat.photos.wild answeredasked 2026-10-22from iNaturalist's open data of 2026-09-27: research-grade observations with an open-licence photograph, the 24 whose photographs iNaturalist received last (the open data holds no votes); filled 2026-10-22
iNaturalist photographs, cultivated inat.photos.cultivated not asked
GBIF media gbif.media answeredasked 2026-10-22read from the page's key and its other keys: 97 from GBIF's key 7820611
OpenAlex papers openalex not askednot yet asked for this reference; a later fill takes the papers from OpenAlex's snapshot

Every source is recorded as having answered, reported nothing, refused, failed, not been asked, or answered twice where one answer is taken (“not taken: two items answered”), and, for a source asked when this page was built, when: the figures are as the source held them that day; a source read from a file (Kew's World Checklist, a GBIF download) says "as of" the file's day instead; a row carried from an earlier build of the page names that build instead. Only “nothing to report” is ever shown as an absence. Records came from 38 datasets via GBIF.org; each carries its own licence.

Cultifolio

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