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Rumex japonicus; photograph (c) Chen Jia Hong, some rights reserved (CC BY) CC BY(c) Chen Jia Hong, some rights reserved (CC BY) · observed growing wild · 2026-03-28

Rumex japonicus Houtt.

Japanese Dock; Northeast Asian curly dock

Polygonaceae · Kamchatka, Kuril Is. +13

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Rumex japonicus, photograph (c) WATANABE Hitoshi 渡辺仁, some rights reserved (CC BY)Rumex japonicus, photograph (c) WATANABE Hitoshi 渡辺仁, some rights reserved (CC BY)Rumex japonicus, photograph (c) 胡正恆(Jackson Hu), some rights reserved (CC BY)Rumex japonicus, photograph (c) Chen Jia Hong, some rights reserved (CC BY)Rumex japonicus, photograph (c) Chen Jia Hong, some rights reserved (CC BY)Rumex japonicus, photograph author not stated, no rights reserved 56 photographs ›
Habitat figures
Cold floor (1 night in 100)
-3.4°C
Record low -8.6 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
28°C
Jul and Aug at the habitat CHELSA
Rain a year (median across the range)
1,878mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
15–35DLI
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
Wet summers: the rain comes April to September, read as a summer growing season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Cultivation

Seasons

The rain rule reads a summer growing season: 70% of the median year's rain (1,368 mm of 1,898 mm) falls in April to September, warmer than the year (wet-season mean 21.5 °C against a yearly mean of 15.9 °C). Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: October to March.

Rain

1,898 mm in the median year at the habitat, 1,368 mm of it April to September. Wettest month August at 289 mm, driest month December at 54 mm. Across the grid cells of the range the year's total runs 1,292 mm to 3,911 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 1,878 mm, is the year's rain at the top of the page; the 1,898 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: 15 to 35 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 13, the highest 90th-percentile month 39).

Warmth and air
Temperature

Coldest: the 1st-percentile night over 44 years at a typical spot in the range is -3.4 °C, the absolute minimum -8.6 °C, 2,266 frost nights in 44 years, 51.5 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 35.2 °C. Monthly means: the coldest month's mean nightly low 2.9 °C in January (across the grid cells of the range -9.3 °C to 14.1 °C), the warmest month's mean daily high 28.4 °C in August (median year across the grid cells of the range, CHELSA). Cold floor: -3.4 °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 66% 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 -206 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 Rumex japonicus through the yearWarmest months July and August, mean daily high 28 °C; coldest month January, mean nightly low 2.9 °C; 1,898 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.-20°-10°0°10°20°30°40°frost35.2° 99th-percentile day, NASA POWER-8.6° lowest night in 44 years, NASA POWER°C · day and nightcold quarter0100200300400500600mm rainDLI 15–35RH 58–66%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 505 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 °C8 / 0–189 / 3–1912 / 7–2118 / 13–2422 / 17–2726 / 21–2928 / 24–3028 / 26–3025 / 22–2820 / 17–2616 / 10–2311 / 3–19
Night °C3 / -9–144 / -7–156 / -2–1611 / 4–2015 / 10–2319 / 15–2522 / 18–2624 / 19–2621 / 15–2515 / 8–2210 / 1–195 / -6–16
Rain mm62 / 23–24186 / 27–263121 / 49–242137 / 70–233184 / 97–334248 / 132–419286 / 167–413289 / 148–408224 / 155–539123 / 46–43284 / 40–35554 / 21–264
DLI17 / 14–2022 / 17–2428 / 23–3033 / 28–3635 / 30–3734 / 30–3633 / 28–3933 / 28–3628 / 25–3124 / 21–2718 / 16–2115 / 13–19
RH %59 / 54–6758 / 54–6759 / 55–6860 / 55–6863 / 57–6865 / 60–7066 / 64–7166 / 63–6964 / 61–6861 / 57–6760 / 56–6659 / 54–66
How this section is made
Each figure is the median across the 505 grid cells on land that hold in-range records (776 records in those cells; 6 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 1092:6388 (35.375, 139.425). Over 44 years there: absolute minimum -8.6 °C, 1st-percentile night -3.4 °C, 99th-percentile day 35.2 °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 505 distinct grid cells holding 776 of the 784 in-range records (6 further cells with records at sea, by the elevation layer, left out); extremes and elevation at the typical cell 1092:6388 (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 35.50_139.375, lapse-corrected -206 m at 6.5 °C/km. Elevation: ETOPO 2022, 27 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.
NativeKamchatka, Kuril Is., Primorye, Sakhalin, China South-Central, Hainan, Inner Mongolia, Manchuria, China Southeast, Japan, Korea, Nansei-shoto, Ogasawara-shoto, Taiwan, Vietnam · 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 marker24.955, 121.497 · in the densest population, 571 records (37% of those in range)
Kew's description“perennial” · “temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 1527 georeferenced records inside the native range; the climate across the range on the 776 of them in the land cells it reads, of 784 placed to within 10 km; the map shows only the 987 openly licensed ones, which alone would put the marker 2053 km away. 11 records outside the WCVP native range not used. 743 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.
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 1527 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Rumex japonicus, photograph 1did not loadRumex japonicus, photograph 2did not loadRumex japonicus, photograph 3did not loadRumex japonicus, photograph 4did not loadRumex japonicus, photograph 5did not loadRumex japonicus, photograph 6did not load

Photographs: (c) WATANABE Hitoshi 渡辺仁, some rights reserved (CC BY) (2); (c) 胡正恆(Jackson Hu), some rights reserved (CC BY); (c) Chen Jia Hong, some rights reserved (CC BY) (2); author not stated, no rights reserved · CC0.

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

Aphananthe aspera Aphananthe aspera Mukutree Photo: CC BY, Licheng ShihMallotus japonicus Mallotus japonicus East Asian mallotus Photo: CC BY, 岸本年郎Ranunculus cantoniensis Ranunculus cantoniensis Canton buttercup Photo: CC BY, 如此甚好Dendropanax trifidus Dendropanax trifidus Araliaceae Photo: CC BY, Saryu Mae 前 朝琉Rhynchosia volubilis Rhynchosia volubilis Winding snoutbean Photo: CC BY-SA, 許文俊Castanopsis sieboldii Castanopsis sieboldii Itajii Photo: CC BY, Jhonatan Matheus

Other Rumex 53 in the reference

Rumex acetosa Rumex acetosa Garden sorrel Photo: CC BY, Nick ButcherRumex acetosella Rumex acetosella Sheep sorrel Photo: CC BY, William HarlandRumex alpinus Rumex alpinus Monk's-rhubarb Photo: CC BY, Tony KMRumex altissimus Rumex altissimus Tall dock Photo: CC BY, BobRumex aquaticus Rumex aquaticus Scottish dock Photo: CC BY, Евгений МаринкинRumex arifolius Rumex arifolius Maiden sorrel Photo: CC BY, Denys VynokurovRumex azoricus Rumex azoricus Azorean Dock Photo: CC BY, LjažRumex britannica Rumex britannica Greater water dock Photo: CC BY, BobRumex brownii Rumex brownii Hooked dock Photo: CC BY-SA, Greg TasneyRumex bucephalophorus Rumex bucephalophorus Horned dock Photo: CC BY, zebedeugalinhaRumex confertus Rumex confertus Russian dock Photo: CC BY, Мирослав СоболевRumex conglomeratus Rumex conglomeratus Clustered dock Photo: CC0, author not stated all 54 ›

Names & registers

Also known as Rumex cardiocarpus; Rumex crispus subsp. japonicus; Rumex crispus var. japonicus; Rumex hadrocarpus; Rumex japonicus var. sachalinensis and 6 more. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataiNaturalist

The record

Family
Polygonaceae
Described by
Houtt.
Native to
Kamchatka, Kuril Is., Primorye +12
Wild records
1527 in range · 987 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 2026-10-22
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 answeredas of 2026-10-21GBIF occurrence download https://doi.org/10.15468/dl.hbdw64, of 2026-10-21; 57 records within 1 km of a botanic garden, herbarium or zoo left out (33 at a botanic garden or arboretum, 14 at a herbarium, 10 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 35.50_139.375, lapse-corrected -206 m at 6.5 °C/km
Wikidata wikidata answeredasked 2026-10-22
Wikipedia wikipedia nothing to reportasked 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 2026-10-22
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 101 datasets via GBIF.org; each carries its own licence.

Cultifolio

Opening your plants…