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Epilobium densiflorum; photograph (c) Alex, some rights reserved (CC BY) CC BY(c) Alex, some rights reserved (CC BY) · observed growing wild · 2026-07-05

Epilobium densiflorum (Lindl.) Hoch & P.H.Raven

Dense-flowered willowherb; Dense spike-primrose; Dense-flowered spike-primrose; Dense-flower Spike-primrose

Onagraceae · British Columbia, Idaho +8

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Epilobium densiflorum, photograph (c) gretchenparadis, some rights reserved (CC BY)Epilobium densiflorum, photograph (c) Dominic Gentilcore, some rights reserved (CC BY)Epilobium densiflorum, photograph (c) Dominic Gentilcore, some rights reserved (CC BY)Epilobium densiflorum, photograph (c) Conquest, some rights reserved (CC BY)Epilobium densiflorum, photograph (c) Conquest, some rights reserved (CC BY)Epilobium densiflorum, photograph (c) Conquest, some rights reserved (CC BY) 86 photographs ›
Habitat figures
Coldest month, mean nightly low
1.4°C
Dec at the habitat, not a floor; extremes not used (the weather cell's ground is too far off) CHELSA
Warmest month, mean daily high
29°C
Jul and Aug at the habitat CHELSA
Rain a year (median across the range)
878mm
8 months of 25 mm or more in the median year CHELSA
Open-sky light
13–52DLI
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 November 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

Epilobium densiflorum is a species of willowherb known by the common names denseflower willowherb, dense spike-primrose or dense boisduvalia. It is native to western North America from British Columbia to Baja California, where it is found in a variety of habitats. This is an erect annual often exceeding a meter in height with fuzzy green foliage. The pointed leaves are up to 8 centimeters long near the base of the plant, and the upper leaves are generally more hairy than the lower. More on Wikipedia ›

Quoted from Wikipedia, "Epilobium densiflorum", CC BY-SA 4.0.

About the genus · Epilobium

Epilobium is a genus of flowering plants in the family Onagraceae, containing about 197 species. The genus has a worldwide distribution. It is most prevalent in the subarctic, temperate and subantarctic regions, whereas in the subtropics and tropics Epilobium species are restricted to the cool montane biomes, such as the New Guinea Highlands.

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

Cultivation

Seasons

The rain rule reads a winter growing season: 70% of the median year's rain (660 mm of 858 mm) falls in November to March, cooler than the year (wet-season mean 6.4 °C against a yearly mean of 12.1 °C). Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: May to September.

Rain

858 mm in the median year at the habitat, 660 mm of it November to March. Wettest month December at 157 mm, driest month July at 6 mm. Across the grid cells of the range the year's total runs 395 mm to 1,542 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 878 mm, is the year's rain at the top of the page; the 858 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: 13 to 52 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 7, the highest 90th-percentile month 54).

Warmth and air
Temperature

Monthly means: the coldest month's mean nightly low 1.4 °C in December (across the grid cells of the range -6.6 °C to 5.0 °C), the warmest month's mean daily high 28.9 °C in July (median year across the grid cells of the range, CHELSA). Cold floor: none read. The nearest figure is 1.4 °C, the coldest month's mean nightly low, December, in the median year (CHELSA); a month's mean of its nightly lows is warmer than the nights a floor is read from. The daily extremes were read at a weather cell whose ground is too far above or below the typical spot to correct for, and are not used.

Humidity

Relative humidity at the habitat: 47 to 61% 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. CHELSA monthly means, median year across the grid cells of the range. No cold floor is read without a daily extremes series; the coldest month's mean nightly low named in its sentence is not one. 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 Epilobium densiflorum through the yearWarmest months July and August, mean daily high 29 °C; coldest month December, mean nightly low 1.4 °C; 858 mm of rain in the median year (the twelve monthly medians added). Medians across the range, from CHELSA. Habitat months, northern hemisphere.-10°0°10°20°30°40°frost°C · day and nightcold quarter050100150200250300mm rainDLI 13–52RH 47–61%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 778 habitat cells, CHELSA cold quarter: the three months around the coldest month's mean nightly low DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C9 / 2–1411 / 3–1614 / 7–1816 / 11–2120 / 16–2625 / 20–3029 / 25–3329 / 24–3325 / 21–3019 / 15–2512 / 7–189 / 1–14
Night °C2 / -6–52 / -6–64 / -3–75 / -1–98 / 3–1211 / 8–1514 / 11–1814 / 11–1812 / 8–158 / 3–124 / -2–81 / -7–5
Rain mm152 / 52–260128 / 47–225111 / 46–19860 / 30–11541 / 12–8018 / 3–526 / 0–187 / 1–1916 / 7–4350 / 23–112112 / 43–225157 / 54–283
DLI14 / 8–1920 / 14–2530 / 21–3539 / 30–4446 / 36–5051 / 40–5452 / 45–5346 / 40–4837 / 30–4026 / 18–3116 / 9–2213 / 7–17
RH %61 / 54–6760 / 55–6458 / 54–6356 / 51–6253 / 48–6050 / 44–5947 / 40–5747 / 41–5749 / 43–5753 / 47–6258 / 52–6760 / 53–67

The daily extremes were not used: the correction for elevation, +1014 m, is beyond the 1,000 m either way that a lapse rate is applied over, so the weather cell's ground is other terrain than the typical spot's. So no cold floor is read for this species, and the coldest month's mean nightly low is not taken as one. What that cell gave, so corrected, over 44 years: absolute minimum -12.4 °C, 1st-percentile night -6.5 °C.

How this section is made
Each figure is the median across the 778 grid cells on land that hold in-range records (1144 records in those cells; 3 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 1161:1283 (31.925, -115.825). 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 778 distinct grid cells holding 1144 of the 1149 in-range records (3 further cells with records at sea, by the elevation layer, left out); extremes and elevation at the typical cell 1161:1283 (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 32.00_-115.625, lapse-corrected +1014 m at 6.5 °C/km. Elevation: ETOPO 2022, 1539 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, Idaho, Montana, Oregon, Washington, Arizona, California, Nevada, Utah, Mexico Northwest · 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 marker38.483, -122.739 · in the densest population, 762 records (50% 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 1535 georeferenced records inside the native range; the climate across the range on the 1144 of them in the land cells it reads, of 1149 placed to within 10 km; the map shows only the 376 openly licensed ones, which alone would put the marker 606 km away. 3 records outside the WCVP native range not used. 386 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 2° block of the 1535 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Epilobium densiflorum, photograph 1did not loadEpilobium densiflorum, photograph 2did not loadEpilobium densiflorum, photograph 3did not loadEpilobium densiflorum, photograph 4did not loadEpilobium densiflorum, photograph 5did not loadEpilobium densiflorum, photograph 6did not load

Photographs: (c) gretchenparadis, some rights reserved (CC BY); (c) Dominic Gentilcore, some rights reserved (CC BY) (2); (c) Conquest, 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.

Nemophila pedunculata Nemophila pedunculata Little-foot nemophila Photo: CC0, author not statedCarex nudata Carex nudata Naked sedge Photo: CC BY, Elly PoretskyCalochortus uniflorus Calochortus uniflorus Monterey mariposa lily Photo: CC BY, wildflowerwatchingDichelostemma congestum Dichelostemma congestum Ookow Photo: CC BY, Parker James LloydMadia gracilis Madia gracilis Slender tarweed Photo: CC BY, Kieran HanrahanAllium amplectens Allium amplectens Slim-leaved onion Photo: CC BY, Parker James Lloyd

Other Epilobium 37 in the reference

Epilobium alpestre Epilobium alpestre Whorled-leaved Willowherb Photo: CC BY, Johannes S.Epilobium alsinifolium Epilobium alsinifolium Chickweed Willowherb Photo: CC BY, Antoine ThivolleEpilobium anagallidifolium Epilobium anagallidifolium Alpine willowherb Photo: CC0, author not statedEpilobium billardiereanum Epilobium billardiereanum Robust willowherb Photo: CC BY, Arnim LittekEpilobium brachycarpum Epilobium brachycarpum Tall annual willowherb Photo: CC BY-SA, Josep GestiEpilobium brunnescens Epilobium brunnescens New Zealand Willowherb Photo: CC BY, James CunninghamEpilobium canum Epilobium canum Hummingbird trumpet Photo: CC BY, Grant ChovilEpilobium ciliatum Epilobium ciliatum American willowherb Photo: CC BY-SA, psweetEpilobium colchicum Epilobium colchicum Onagraceae Photo: CC BY, Алина УрусоваEpilobium coloratum Epilobium coloratum Cinnamon willowherb Photo: CC BY, Jeff ClarkEpilobium crassum Epilobium crassum Onagraceae Photo: CC0, author not statedEpilobium dodonaei Epilobium dodonaei Onagraceae Photo: CC BY, Philipendula all 38 ›

Names & registers

Also known as Boisduvalia bipartita; Boisduvalia densiflora; Boisduvalia densiflora f. imbricata; Boisduvalia densiflora var. bipartita; Boisduvalia densiflora var. genuina and 12 more. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Onagraceae
Described by
(Lindl.) Hoch & P.H.Raven
Native to
British Columbia, Idaho, Montana +7
Wild records
1535 in range · 376 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; 23 records within 1 km of a botanic garden, herbarium or zoo left out (15 at a botanic garden or arboretum, 3 at a herbarium, 5 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 32.00_-115.625, lapse-corrected +1014 m at 6.5 °C/km; read, and set aside: the correction for elevation, +1014 m, is beyond the 1,000 m either way that a lapse rate is applied over, so the weather cell's ground is other terrain than the typical spot's, so no cold floor is shown
Wikidata wikidata answeredasked 2026-10-22IPNI and POWO linked by Kew's number for Epilobium densiflorum (Lindl.) Hoch & P.H.Raven (the item's: IPNI 1202019-2, POWO 969682-1)
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 66 datasets via GBIF.org; each carries its own licence.

Cultifolio

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