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Paspalum distichum; photograph (c) Augustin Soulard, some rights reserved (CC BY) CC BY(c) Augustin Soulard, some rights reserved (CC BY) · observed growing wild · 2026-09-09

Paspalum distichum L.

Knotgrass; Water finger-grass; Water couch; Couch paspalum

Poaceae · Idaho, Oregon +68

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Paspalum distichum, photograph (c) Augustin Soulard, some rights reserved (CC BY)Paspalum distichum, photograph (c) Augustin Soulard, some rights reserved (CC BY)Paspalum distichum, photograph (c) Augustin Soulard, some rights reserved (CC BY)Paspalum distichum, photograph (c) Augustin Soulard, some rights reserved (CC BY)Paspalum distichum, photograph (c) petitcrabe, some rights reserved (CC BY)Paspalum distichum, photograph (c) petitcrabe, some rights reserved (CC BY) 120 photographs ›
Habitat figures
Cold floor (1 night in 100)
-0.4°C
Record low -6.8 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
30°C
Jul and Aug at the habitat CHELSA
Rain a year (median across the range)
606mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
19–47DLI
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

Paspalum distichum is a species of grass. Common names include knotgrass, water finger-grass, couch paspalum, eternity grass, gingergrass, and Thompson grass. Its native range is obscure because it has long been present on most continents, and in most areas it is certainly an introduced species. Its native range probably includes parts of the tropical Americas.

Quoted from Wikipedia, "Paspalum distichum", CC BY-SA 4.0.

Cultivation

Seasons

The rain rule reads no short rainy season: 70% of the median year's rain (426 mm of 565 mm) takes 8 months, December to March and June to September. Mean temperature moves 15.0 °C between the warmest and coldest month. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: December to March and June to September.

Rain

565 mm in the median year at the habitat, 426 mm of it December to March and June to September. Wettest month February at 67 mm, driest month May at 31 mm. Across the grid cells of the range the year's total runs 302 mm to 1,454 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 606 mm, is the year's rain at the top of the page; the 565 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: 19 to 47 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 12, the highest 90th-percentile month 53).

Warmth and air
Temperature

Coldest: the 1st-percentile night over 44 years at a typical spot in the range is -0.4 °C, the absolute minimum -6.8 °C, 207 frost nights in 44 years, 4.7 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 43.4 °C. Monthly means: the coldest month's mean nightly low 4.3 °C in January (across the grid cells of the range -2.3 °C to 9.4 °C), the warmest month's mean daily high 30.4 °C in July and August (median year across the grid cells of the range, CHELSA). Cold floor: -0.4 °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: 52 to 57% 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 -278 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 Paspalum distichum through the yearWarmest months July and August, mean daily high 30 °C; coldest month January, mean nightly low 4.3 °C; 565 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.-10°0°10°20°30°40°50°frost43.4° 99th-percentile day, NASA POWER-6.8° lowest night in 44 years, NASA POWER°C · day and nightcold quarter050100150200mm rainDLI 19–47RH 52–57%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 66 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 °C14 / 8–2216 / 10–2419 / 13–2623 / 17–2827 / 20–3029 / 22–3330 / 22–3430 / 23–3428 / 22–3124 / 19–2719 / 13–2514 / 8–23
Night °C4 / -2–96 / -1–108 / 3–1310 / 6–1513 / 9–1815 / 12–2218 / 12–2417 / 13–2416 / 12–2112 / 8–178 / 3–135 / -2–10
Rain mm50 / 15–15167 / 12–14047 / 6–13534 / 9–10631 / 7–11749 / 3–14560 / 0–19757 / 1–18751 / 6–15041 / 20–12633 / 12–12745 / 9–159
DLI20 / 14–3226 / 20–3834 / 28–4541 / 35–4847 / 37–5146 / 39–5345 / 38–5341 / 37–4836 / 31–3929 / 24–3423 / 15–3319 / 12–30
RH %57 / 49–6357 / 47–6355 / 44–6353 / 41–6152 / 43–6256 / 42–6356 / 45–6456 / 47–6457 / 46–6556 / 47–6356 / 48–6257 / 49–63
How this section is made
Each figure is the median across the 66 grid cells holding the 67 in-range records, 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 1016:1169 (39.175, -121.525). Over 44 years there: absolute minimum -6.8 °C, 1st-percentile night -0.4 °C, 99th-percentile day 43.4 °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 66 distinct grid cells holding 67 of the 67 in-range records; extremes and elevation at the typical cell 1016:1169 (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 39.00_-121.250, lapse-corrected -278 m at 6.5 °C/km. Elevation: ETOPO 2022, 26 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.
NativeIdaho, Oregon, Washington, Kansas, Missouri, Oklahoma, New Jersey, Pennsylvania, Arizona, California, Nevada, Utah, New Mexico, Texas, Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, Mexico Central, Mexico Northeast, Mexico Gulf, Mexico Northwest, Mexico Southwest, Mexico Southeast, Costa Rica, C. American Pacific Is., El Salvador, Guatemala, Honduras, Nicaragua, Bahamas, Bermuda, Cuba, Dominican Republic, Haiti, Jamaica, Leeward Is. AB Ant, Puerto Rico, Turks-Caicos Is., Trinidad-Tobago, Windward Is., Guyana, Surinam, Venezuela, Bolivia, Colombia, Ecuador, Galápagos, Peru, Brazil West-Central, Brazil Northeast, Brazil Southeast, Brazil North, Brazil South, Argentina Northeast, Argentina South, Argentina Northwest, Chile Central, Chile North, Juan Fernández Is., Paraguay, Uruguay · introduced: Great Britain, Austria, Belgium, Germany, France, Portugal, Sardegna, Spain, Albania, Bulgaria, Greece, Italy, Romania, Turkey-in-Europe, Krym, Algeria, Egypt, Libya, Morocco, Tunisia, Azores, Canary Is., Madeira, Mauritania, Togo, Zaïre, Zimbabwe, Cape Provinces, Lesotho, Namibia, KwaZulu-Natal, Free State, Swaziland, Northern Provinces, Aldabra, Comoros, Mauritius, Réunion, Tadzhikistan, Transcaucasus, Cyprus, East Aegean Is., Iran, Iraq, Lebanon-Syria, Palestine, Sinai, Turkey, Oman, Saudi Arabia, Yemen, China South-Central, Hainan, China North-Central, China Southeast, Japan, Korea, Nansei-shoto, Taiwan, Assam, Bangladesh, East Himalaya, India, Maldives, Nepal, Pakistan, Sri Lanka, West Himalaya, Andaman Is., Cambodia, Myanmar, South China Sea, Vietnam, Borneo, Jawa, Malaya, Maluku, Philippines, Sulawesi, Norfolk Is., New South Wales, Queensland, South Australia, Tasmania, Victoria, Western Australia, Kermadec Is., New Zealand North, New Zealand South, Fiji, New Caledonia, Samoa, Tuvalu, Vanuatu, Cook Is., Hawaii, Indiana · 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 marker39.355, -121.516 · in the densest population, 46 records (28% of those in range)
Kew's description“rhizomatous geophyte” · “seasonally dry tropical” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 163 georeferenced records inside the native range; the climate across the range on the 67 of them placed to within 10 km; the map shows only the 103 openly licensed ones, which alone would put the marker 2745 km away. 1268 records outside the WCVP native range not used. 96 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 163 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Paspalum distichum, photograph 1did not loadPaspalum distichum, photograph 2did not loadPaspalum distichum, photograph 3did not loadPaspalum distichum, photograph 4did not loadPaspalum distichum, photograph 5did not loadPaspalum distichum, photograph 6did not load

Photographs: (c) Augustin Soulard, some rights reserved (CC BY) (4); (c) petitcrabe, some rights reserved (CC BY) (2).

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

Cucurbita foetidissima Cucurbita foetidissima Buffalo gourd Photo: CC BY, Aiva NoringsethEleocharis montevidensis Eleocharis montevidensis Sand spike-rush Photo: CC0, author not statedMarsilea vestita Marsilea vestita Hairy water-clover Photo: CC BY, Sam KieschnickSchoenoplectus americanus Schoenoplectus americanus Chairmaker's bulrush Photo: CC BY, Daughter DadSelaginella peruviana Selaginella peruviana Peruvian spikemoss Photo: CC BY, Sam KieschnickBothriochloa barbinodis Bothriochloa barbinodis Cane bluestem Photo: CC BY, mel letterman

Other Paspalum 15 in the reference

Paspalum conjugatum Paspalum conjugatum Hilo grass Photo: CC0, author not statedPaspalum dilatatum Paspalum dilatatum Dallis-grass Photo: CC BY, fmunozPaspalum floridanum Paspalum floridanum Florida paspalum Photo: CC BY, Brandon CorderPaspalum laeve Paspalum laeve Field paspalum Photo: CC BY, Bryan ConnollyPaspalum langei Paspalum langei Rusty-seed paspalum Photo: CC0, author not statedPaspalum notatum Paspalum notatum Bahia grass Photo: CC BY, 祐Paspalum paniculatum Paspalum paniculatum Russell River grass Photo: CC BY, GabrielPaspalum plicatulum Paspalum plicatulum Brown-seed paspalum Photo: CC0, author not statedPaspalum pubiflorum Paspalum pubiflorum Hairy-seed paspalum Photo: CC BY, Chris StahlPaspalum quadrifarium Paspalum quadrifarium Tussock paspalum Photo: CC0, author not stated Paspalum racemosum Peruvian paspalum Paspalum repens Paspalum repens Water paspalum Photo: CC BY, Ryan Sorrells all 16 ›

Names & registers

Also known as Anastrophus paspalodes; Anastrophus paspaloides; Digitaria disticha; Digitaria paspalodes; Digitaria paspaloides and 43 more. (GBIF Backbone)

Under another author Paspalum vaginatum Döll is an older name of this species, not Paspalum vaginatum, a species of the reference. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Poaceae
Described by
L.
Native to
Idaho, Oregon, Washington +67
Wild records
163 in range · 103 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; 16 records within 1 km of a botanic garden, herbarium or zoo left out (12 at a botanic garden or arboretum, 4 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 39.00_-121.250, lapse-corrected -278 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 2026-10-22
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 276 datasets via GBIF.org; each carries its own licence.

Cultifolio

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