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Sagittaria filiformis; photograph (c) Athena Philips, some rights reserved (CC BY) CC BY(c) Athena Philips, some rights reserved (CC BY) · observed growing wild · 2025-09-06

Sagittaria filiformis J.G.Sm.

Threadleaf arrowhead

Alismataceae · Connecticut, Maine +10

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Sagittaria filiformis, photograph (c) Patrick Belk, some rights reserved (CC BY)Sagittaria filiformis, photograph (c) Patrick Belk, some rights reserved (CC BY)Sagittaria filiformis, photograph (c) Patrick Belk, some rights reserved (CC BY)Sagittaria filiformis, photograph (c) Athena Philips, some rights reserved (CC BY)Sagittaria filiformis, photograph (c) Athena Philips, some rights reserved (CC BY)Sagittaria filiformis, photograph (c) Athena Philips, some rights reserved (CC BY) 31 photographs ›
Habitat figures
Cold floor (1 night in 100)
1.4°C
Record low -7.9 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
32°C
Jul at the habitat CHELSA
Rain a year (median across the range)
1,318mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
19–41DLI
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 February to March and June to October, read as a summer growing season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Summary

Sagittaria filiformis, the threadleaf arrowhead, is a perennial aquatic plant growing up to 170 centimetres (67 inches) tall. Some leaves are thread-like, entirely underwater, but others are narrowly ovate or lanceolate and floating on the surface.

Quoted from Wikipedia, "Sagittaria filiformis", CC BY-SA 4.0.

Cultivation

Seasons

The rain rule reads a summer growing season: 70% of the median year's rain (969 mm of 1,324 mm) falls in February to March and June to October, warmer than the year (wet-season mean 22.6 °C against a yearly mean of 20.5 °C). Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: December to April and August to September.

Rain

1,324 mm in the median year at the habitat, 969 mm of it February to March and June to October. Wettest month August at 185 mm, driest month November at 60 mm. Across the grid cells of the range the year's total runs 1,233 mm to 1,435 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 1,318 mm, is the year's rain at the top of the page; the 1,324 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 41 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 11, 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 1.4 °C, the absolute minimum -7.9 °C, 84 frost nights in 44 years, 1.9 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 34.6 °C. Monthly means: the coldest month's mean nightly low 8.7 °C in January (across the grid cells of the range -3.8 °C to 12.2 °C), the warmest month's mean daily high 31.6 °C in July (median year across the grid cells of the range, CHELSA). Cold floor: 1.4 °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: 57 to 64% 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 -2 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 Sagittaria filiformis through the yearWarmest month July, mean daily high 32 °C; coldest month January, mean nightly low 8.7 °C; 1,324 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°frost34.6° 99th-percentile day, NASA POWER-7.9° lowest night in 44 years, NASA POWER°C · day and nightcold quarter050100150200250mm rainDLI 19–41RH 57–64%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 65 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 °C18 / 3–2120 / 4–2223 / 9–2426 / 15–2729 / 20–3031 / 25–3232 / 28–3231 / 27–3230 / 23–3127 / 17–2823 / 11–2519 / 6–22
Night °C9 / -4–1210 / -3–1313 / 1–1516 / 6–1819 / 11–2123 / 17–2424 / 20–2524 / 20–2522 / 16–2419 / 11–2115 / 5–1710 / 0–14
Rain mm81 / 61–11583 / 67–113105 / 92–13671 / 60–10373 / 62–99180 / 107–205176 / 110–212185 / 109–212153 / 104–19187 / 69–11960 / 48–10270 / 62–108
DLI21 / 14–2225 / 20–2732 / 26–3339 / 32–4041 / 37–4338 / 38–4038 / 37–4034 / 33–3630 / 28–3127 / 21–2822 / 14–2319 / 11–20
RH %58 / 57–5958 / 56–5957 / 56–5957 / 56–5858 / 57–6162 / 59–6463 / 60–6564 / 61–6663 / 60–6460 / 58–6159 / 57–5958 / 57–59
How this section is made
Each figure is the median across the 65 grid cells holding the 78 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 1166:1977 (31.675, -81.125). Over 44 years there: absolute minimum -7.9 °C, 1st-percentile night 1.4 °C, 99th-percentile day 34.6 °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 65 distinct grid cells holding 78 of the 78 in-range records; extremes and elevation at the typical cell 1166:1977 (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 31.50_-81.250, lapse-corrected -2 m at 6.5 °C/km. Elevation: ETOPO 2022, 3 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.
NativeConnecticut, Maine, Massachusetts, New York, Pennsylvania, Rhode I., Alabama, Florida, Georgia, North Carolina, South Carolina, Virginia · introduced: Trinidad-Tobago · 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 marker28.583, -82.217 · in the densest population, 85 records (54% of those in range)
Kew's description“helophyte or tuberous geophyte” · “temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 158 georeferenced records inside the native range; the climate across the range on the 78 of them placed to within 10 km; the map shows only the 82 openly licensed ones, which alone would put the marker 15 km away. 3 records outside the WCVP native range not used. 80 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 of the 158 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Sagittaria filiformis, photograph 1did not loadSagittaria filiformis, photograph 2did not loadSagittaria filiformis, photograph 3did not loadSagittaria filiformis, photograph 4did not loadSagittaria filiformis, photograph 5did not loadSagittaria filiformis, photograph 6did not load

Photographs: (c) Patrick Belk, some rights reserved (CC BY) (3); (c) Athena Philips, some rights reserved (CC BY) (3).

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

Gaylussacia tomentosa Gaylussacia tomentosa Blue huckleberry Photo: CC BY, Daniel FarsonAgarista populifolia Agarista populifolia Pipe-plant Photo: CC BY, aispinsectsHoustonia procumbens Houstonia procumbens Innocence Photo: CC BY, James HardeePycnanthemum floridanum Pycnanthemum floridanum Florida mountain-mint Photo: CC BY, carterDalea pinnata Dalea pinnata Summer farewell Photo: CC0, author not statedIndigofera caroliniana Indigofera caroliniana Carolina indigo Photo: CC0, author not stated

Other Sagittaria 18 in the reference

Sagittaria calycina Sagittaria calycina Alismataceae Photo: CC BY, Dan JohnsonSagittaria cuneata Sagittaria cuneata Northern arrowhead Photo: CC BY, Arthur WhitingSagittaria graminea Sagittaria graminea Grass-leaved arrowhead Photo: CC BY, Patrick JacksonSagittaria guayanensis Sagittaria guayanensis Guyanese arrowhead Photo: CC BY, Non_Praying_MantisSagittaria intermedia Sagittaria intermedia Intermediate arrowhead Photo: CC BY, PatrickSagittaria lancifolia Sagittaria lancifolia Bulltongue Photo: CC0, author not statedSagittaria latifolia Sagittaria latifolia Duck-potato Photo: CC BY, Mandatory WalkSagittaria longiloba Sagittaria longiloba Longbarb arrowhead Photo: CC BY, Claudio Cantú Muñiz Sagittaria macrophylla Alismataceae Sagittaria montevidensis Sagittaria montevidensis Giant arrowhead Photo: CC BY, Pablo H CapovillaSagittaria natans Sagittaria natans Floating arrowhead Photo: CC BY, Valerii GlazunovSagittaria platyphylla Sagittaria platyphylla Delta arrowhead Photo: CC BY, Jay Pruett all 19 ›

Names & registers

Also known as Sagittaria natans var. gracillima; Sagittaria stagnorum; Sagittaria subulata var. gracillima; Sagittaria subulata var. natans. (GBIF Backbone)

Under another author Sagittaria natans Michx. is an older name of this species, not Sagittaria natans, a species of the reference. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Alismataceae
Described by
J.G.Sm.
Native to
Connecticut, Maine, Massachusetts +9
Wild records
158 in range · 82 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; 1 record within 1 km of a botanic garden, herbarium or zoo left out (1 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 31.50_-81.250, lapse-corrected -2 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
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 26 datasets via GBIF.org; each carries its own licence.

Cultifolio

Opening your plants…