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Myriophyllum hippuroides; photograph (c) Gabriel Campbell-Martinez, some rights reserved (CC BY) CC BY(c) Gabriel Campbell-Martinez, some rights reserved (CC BY) · observed growing wild · 2025-07-01

Myriophyllum hippuroides Nutt.

Western water-milfoil

Haloragaceae · British Columbia, Oregon +5

Cited as Kew's World Checklist cites it, Myriophyllum hippuroides Nutt.: GBIF's backbone key for this page carries the name with another author, Nutt. ex Torr. & A.Gray.

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Myriophyllum hippuroides, photograph (c) Gabriel Campbell-Martinez, some rights reserved (CC BY)Myriophyllum hippuroides, photograph (c) Gabriel Campbell-Martinez, some rights reserved (CC BY)Myriophyllum hippuroides, photograph (c) Nolan Exe, some rights reserved (CC BY)Myriophyllum hippuroides, photograph (c) Nolan Exe, some rights reserved (CC BY)Myriophyllum hippuroides, photograph (c) Lee Cain, some rights reserved (CC BY)Myriophyllum hippuroides, photograph (c) Lee Cain, some rights reserved (CC BY) 13 photographs ›
Habitat figures
Cold floor (1 night in 100)
0.1°C
Record low -4.0 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
26°C
Jul and Aug at the habitat CHELSA
Rain a year (median across the range)
1,329mm
10 months of 25 mm or more in the median year CHELSA
Open-sky light
8–45DLI
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 winters: the rain comes October to March, read as a winter growing season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Summary

Myriophyllum hippuroides is a species of watermilfoil known by the common name western watermilfoil. It is native to the west coast of North America, where it grows in aquatic habitat such as ponds and streams. It generally grows over a meter long, with its stem lined with whorls of fleshy green leaves divided into many narrow lobes. The leafy inflorescence is a spike of small flowers up to 12 centimeters (4.7 in) long which grows above the water's surface.

Quoted from Wikipedia, "Myriophyllum hippuroides", CC BY-SA 4.0.

About the genus · Myriophyllum

Myriophyllum is a genus of about 69 species of freshwater aquatic plants, with a cosmopolitan distribution. The centre of diversity for Myriophyllum is Australia with 43 recognized species.

Quoted from Wikipedia, "Myriophyllum", CC BY-SA 4.0.

Cultivation

Seasons

The rain rule reads a winter growing season: 70% of the median year's rain (1,021 mm of 1,338 mm) falls in October to March, cooler than the year (wet-season mean 9.0 °C against a yearly mean of 12.4 °C). Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: April to September.

Rain

1,338 mm in the median year at the habitat, 1,021 mm of it October to March. Wettest month December at 222 mm, driest month July at 16 mm. Across the grid cells of the range the year's total runs 570 mm to 2,166 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 1,329 mm, is the year's rain at the top of the page; the 1,338 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: 8 to 45 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 6, 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 0.1 °C, the absolute minimum -4.0 °C, 154 frost nights in 44 years, 3.5 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 29.9 °C. Monthly means: the coldest month's mean nightly low 3.9 °C in January (across the grid cells of the range 0.7 °C to 6.8 °C), the warmest month's mean daily high 26.1 °C in August (median year across the grid cells of the range, CHELSA). Cold floor: 0.1 °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 65% 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 -55 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 Myriophyllum hippuroides through the yearWarmest months July and August, mean daily high 26 °C; coldest month January, mean nightly low 3.9 °C; 1,338 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°frost29.9° 99th-percentile day, NASA POWER-4.0° lowest night in 44 years, NASA POWER°C · day and nightcold quarter0100200300400mm rainDLI 8–45RH 58–65%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 92 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 °C11 / 8–1912 / 9–2113 / 11–2316 / 13–2519 / 15–2723 / 17–3226 / 18–3326 / 19–3223 / 18–3018 / 15–2613 / 10–2010 / 7–20
Night °C4 / 1–74 / 1–76 / 3–87 / 5–109 / 8–1311 / 10–1713 / 11–1913 / 12–1812 / 10–169 / 7–126 / 3–94 / 0–7
Rain mm197 / 18–336150 / 14–256141 / 11–25697 / 20–17076 / 25–11461 / 8–14616 / 1–19919 / 2–16648 / 9–135110 / 34–159201 / 19–332222 / 10–384
DLI10 / 8–3215 / 13–3823 / 20–4432 / 29–4639 / 35–4741 / 37–5245 / 38–5340 / 36–4832 / 28–3820 / 16–3311 / 8–328 / 6–31
RH %64 / 53–6963 / 52–6663 / 49–6561 / 50–6460 / 49–6559 / 47–6658 / 45–6758 / 45–6760 / 47–6662 / 51–6565 / 56–6964 / 54–69
How this section is made
Each figure is the median across the 92 grid cells on land that hold in-range records (113 records in those cells; 1 more cell holds records but no land by the elevation layer, so those records sit at sea and the cell is 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 1414:1609 (19.275, -99.525). Over 44 years there: absolute minimum -4.0 °C, 1st-percentile night 0.1 °C, 99th-percentile day 29.9 °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 92 distinct grid cells holding 113 of the 114 in-range records (1 further cell with records at sea, by the elevation layer, left out); extremes and elevation at the typical cell 1414:1609 (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 19.50_-99.375, lapse-corrected -55 m at 6.5 °C/km. Elevation: ETOPO 2022, 2572 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.
NativeBritish Columbia, Oregon, Washington, California, Mexico Central, Mexico Northeast, Mexico Southwest · introduced: Sweden, Illinois, Cuba · 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 marker44.397, -123.302 · in the densest population, 146 records (68% of those in range)
Kew's description“helophyte” · “temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 215 georeferenced records inside the native range; the climate across the range on the 113 of them in the land cells it reads, of 114 placed to within 10 km; the map shows only the 124 openly licensed ones, which alone would put the marker 256 km away. 6 records outside the WCVP native range not used. 101 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 7451893 (Myriophyllum hippuroides Nutt.): Kew's file holds it as Myriophyllum hippuroides Nutt. (accepted); 50 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 215 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Myriophyllum hippuroides, photograph 1did not loadMyriophyllum hippuroides, photograph 2did not loadMyriophyllum hippuroides, photograph 3did not loadMyriophyllum hippuroides, photograph 4did not loadMyriophyllum hippuroides, photograph 5did not loadMyriophyllum hippuroides, photograph 6did not load

Photographs: (c) Gabriel Campbell-Martinez, some rights reserved (CC BY) (2); (c) Nolan Exe, some rights reserved (CC BY) (2); (c) Lee Cain, 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.

Clarkia amoena Clarkia amoena Godetia Photo: CC0, author not statedAnarrhinum duriminium Anarrhinum duriminium Plantaginaceae Photo: CC BY, zebedeugalinhaTriphysaria pusilla Triphysaria pusilla Dwarf owl's-clover Photo: CC BY, Dee Shea HimesAllium scorzonerifolium Allium scorzonerifolium Amaryllidaceae Photo: CC BY, Celestino Quintela Sabarís Cistus lasianthus Cistaceae Echium rosulatum Echium rosulatum Lax Viper's-bugloss Photo: CC BY, jwor

Other Myriophyllum 16 in the reference

Myriophyllum alterniflorum Myriophyllum alterniflorum Alternate Water-milfoil Photo: CC BY, Ewan ShillandMyriophyllum aquaticum Myriophyllum aquaticum Parrot's feather Photo: CC0, author not statedMyriophyllum crispatum Myriophyllum crispatum Upright water-milfoil Photo: CC BY, Eamonn CulhaneMyriophyllum heterophyllum Myriophyllum heterophyllum Broadleaf water-milfoil Photo: CC0, author not statedMyriophyllum mattogrossense Myriophyllum mattogrossense Haloragaceae Photo: Public domain, TsunamiCarlosMyriophyllum papillosum Myriophyllum papillosum Haloragaceae Photo: CC BY, Richard HartlandMyriophyllum pinnatum Myriophyllum pinnatum Cut-leaved water-milfoil Photo: CC BY, Andy JordanMyriophyllum propinquum Myriophyllum propinquum Haloragaceae Photo: CC0, author not statedMyriophyllum quitense Myriophyllum quitense Andean water milfoil Photo: CC BY, Mirko DuimichMyriophyllum rubricaule Myriophyllum rubricaule Red-stemmed Parrot's Feather Photo: CC BY, Stefan EhlMyriophyllum sibiricum Myriophyllum sibiricum Siberian water-milfoil Photo: CC0, author not statedMyriophyllum simulans Myriophyllum simulans Amphibious Water Milfoil Photo: CC BY, Bryce Watts-Parker all 17 ›

Names & registers

Also known as Myriophyllum scabratum. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Haloragaceae
Described by
Nutt.
Native to
British Columbia, Oregon, Washington +4
Wild records
215 in range · 124 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 5361772 is Myriophyllum hippuroides Nutt. ex Torr. & A.Gray; the page links Kew's Myriophyllum hippuroides Nutt., 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 download https://doi.org/10.15468/dl.hbdw64, of 2026-10-21; 50 records of GBIF's key 7451893, Myriophyllum hippuroides Nutt. (Kew's file holds it as Myriophyllum hippuroides Nutt. (accepted)): GBIF occurrence search API; 3 records within 1 km of a botanic garden, herbarium or zoo left out (3 at a botanic garden or arboretum; 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 19.50_-99.375, lapse-corrected -55 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 2026-10-22none of the photographs on this page is credited to GBIF: those shown are other sources', and GBIF's were the same photographs or were set aside by the photograph rules
Wikimedia Commons commons 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 40 datasets via GBIF.org; each carries its own licence.

Cultifolio

Opening your plants…