Epilobium tetragonumL.

square-stemmed willowherb

WFO wfo-0000669847 Accepted WFO 2026-06 8 photographs CC0 / CC BY

Plate 1 figs. a–h · 8 separate observations

Epilobium tetragonum, photographed by Pavel Kacl
fig. a Pavel Kacl, CC BY 4.0 / 2022-06-11 / obs. 205272859
Epilobium tetragonum, photographed by Tim Kirsten
fig. b Tim Kirsten, CC0 1.0 / obs. 174101766
Epilobium tetragonum, photographed by Jeremy Gilmore
fig. c Jeremy Gilmore, CC BY 4.0 / obs. 158875704
Epilobium tetragonum, photographed by Aleksei Baushev
fig. d Aleksei Baushev, CC BY 4.0 / obs. 153752346
Epilobium tetragonum, photographed by Dmitriy Bochkov
fig. e Dmitriy Bochkov, CC BY 4.0 / obs. 163808143
Epilobium tetragonum, photographed by Aleksei Baushev
fig. f Aleksei Baushev, CC BY 4.0 / obs. 150743540
Epilobium tetragonum, photographed by Aleksei Baushev
fig. g Aleksei Baushev, CC BY 4.0 / obs. 150723668
Epilobium tetragonum, photographed by Robert H. Wardell
fig. h Robert H. Wardell, CC0 1.0 / obs. 147302070

Every figure is a research-grade observation under CC0, CC BY or CC BY-SA, rehosted with the photographer’s name, the licence and the observation it came from. Photographs under a NonCommercial licence are excluded from this site and are never stored, which costs us a great many pictures and is not negotiable.

Native range 60 botanical countries

Regions where Epilobium tetragonum is native: Algeria, Azores, Canary Is., Cape Provinces, Free State, KwaZulu-Natal, Lesotho, Madeira, Morocco, Northern Provinces, Tunisia, Altay, Cyprus, East Aegean Is., Iran, Kazakhstan, Kirgizstan, Krasnoyarsk, Lebanon-Syria, North Caucasus, Palestine, Tadzhikistan, Transcaucasus, Türkiye, Turkmenistan, Uzbekistan, West Siberia, West Himalaya, Albania, Austria, Baleares, Baltic States, Belarus, Belgium, Bulgaria, Central European Russia, Corse, Czechia-Slovakia, East European Russia, France, Germany, Great Britain, Greece, Hungary, Ireland, Italy, Kriti, Netherlands, Northwest European Russia, NW. Balkan Pen., Poland, Portugal, Romania, Sardegna, Sicilia, South European Russia, Spain, Switzerland, Türkiye-in-Europe, Ukraine AlgeriaCape ProvincesFree StateKwaZulu-NatalLesothoMoroccoNorthern ProvincesTunisiaAltayCyprusEast Aegean Is.IranKazakhstanKirgizstanKrasnoyarskLebanon-SyriaNorth CaucasusPalestineTadzhikistanTranscaucasusTürkiyeTurkmenistanUzbekistanWest SiberiaWest HimalayaAlbaniaAustriaBaltic StatesBelarusBelgiumBulgariaCentral European RussiaCorseCzechia-SlovakiaEast European RussiaFranceGermanyGreeceHungaryIrelandItalyKritiNetherlandsNorthwest European RussiaNW. Balkan Pen.PolandPortugalRomaniaSiciliaSouth European RussiaSpainSwitzerlandTürkiye-in-EuropeUkraine AzoresCanary Is.MadeiraBalearesSardegna
Native distribution of Epilobium tetragonum, after Kew’s World Checklist of Vascular Plants. Introduced, extinct and doubtful records are excluded, so this is where the plant is from, not everywhere it now grows. Regions too small to draw at this scale are marked with a dot.
RegionTDWG codeContinent
Albania ALB EUROPE
Austria AUT
Baleares BAL
Baltic States BLT
Belarus BLR
Belgium BGM
Bulgaria BUL
Central European Russia RUC
Corse COR
Czechia-Slovakia CZE
East European Russia RUE
France FRA
Germany GER
Great Britain GRB
Greece GRC
Hungary HUN
Ireland IRE
Italy ITA
Kriti KRI
Netherlands NET
Northwest European Russia RUW
NW. Balkan Pen. YUG
Poland POL
Portugal POR
Romania ROM
Sardegna SAR
Sicilia SIC
South European Russia RUS
Spain SPA
Switzerland SWI
Türkiye-in-Europe TUE
Ukraine UKR
Altay ALT ASIA-TEMPERATE
Cyprus CYP
East Aegean Is. EAI
Iran IRN
Kazakhstan KAZ
Kirgizstan KGZ
Krasnoyarsk KRA
Lebanon-Syria LBS
North Caucasus NCS
Palestine PAL
Tadzhikistan TZK
Transcaucasus TCS
Türkiye TUR
Turkmenistan TKM
Uzbekistan UZB
West Siberia WSB
Algeria ALG AFRICA
Azores AZO
Canary Is. CNY
Cape Provinces CPP
Free State OFS
KwaZulu-Natal NAT
Lesotho LES
Madeira MDR
Morocco MOR
Northern Provinces TVL
Tunisia TUN
West Himalaya WHM ASIA-TROPICAL

Not drawn on the map: Great Britain. We hold no public-domain boundary for this region, so it is listed rather than guessed at.

Region boundaries approximated from Natural Earth (public domain) and mapped to TDWG World Geographical Scheme for Recording Plant Distributions (WGSRPD) level-3 botanical countries (Brummitt 2001). Indicative, not the official WGSRPD geometry.

Flowering 63 in flower of 72 examined

Peak flowering in Jul. Each bar is the share of Epilobium tetragonum observations in which someone actually recorded the reproductive state and found the plant in flower, not the raw number of flowering records. That distinction matters: people observe plants far more in spring than in winter, so a bare count of flowering records partly measures when people go outside. Dividing by the number examined removes that. 63 of 72 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 8 months have fewer than 5 examined observations, so no proportion is drawn for them. This is still a global aggregate and not a forecast for your garden: the same species flowers on different dates in different hemispheres. Where a species has fewer than 30 flowering records we do not draw this chart at all. Computed from 10.15468/dl.cgje2x.

Where it actually grows measured, from 827 observations

Condition 5th percentile Median 95th percentile
Coldest month, mean daily low -12.6 °C -6.1 °C 7.0 °C
Warmest month, mean daily high 20.2 °C 23.5 °C 28.0 °C
Annual rainfall 513 mm 663 mm 1,159 mm
Rainfall in the driest quarter 75 mm 111 mm 199 mm

It is found where winters bring hard frost. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 827 research-grade observations of Epilobium tetragonum that carry a coordinate, and this is the range those places actually span. The 5th and 95th percentiles are used rather than the minimum and maximum, because a single cultivated specimen in a heated conservatory should not widen a tropical plant's range to the Arctic.

This is not a hardiness zone. A USDA zone is the average annual extreme minimum temperature. The figure above is the mean daily minimum of the coldest month, which is a different quantity and is typically far warmer. Reading one as the other would place a plant several zones too warm, so we do not publish a hardiness zone, because we do not have one. Climate from CHELSA V2.1 (Karger et al. 2017); occurrences from 10.15468/dl.cgje2x.

Also published as 52 synonyms

A synonym is not an error. It is a record of botanists disagreeing, in print, about where this plant belongs. Each of these was somebody’s considered answer.

  • Chamaenerion tetragonum (L.) Scop.
  • Epilobium adnatoparviflorum Griseb.
  • Epilobium adnatum Griseb.
  • Epilobium adnatum f. major Hausskn.
  • Epilobium adnatum f. rodriguezii Hausskn.
  • Epilobium adnatum f. simplex Hausskn.
  • Epilobium adnatum f. stenophylla Hausskn.
  • Epilobium adnatum prol. tournefortii (Michalet) Samp.
  • Epilobium adnatum var. henriquesii H.Lév.
  • Epilobium adnatum var. heribaudii H.Lév.
  • Epilobium adnatum var. rodriguezii Sennen
  • Epilobium adnatum var. rodriguezii (Hausskn.) Sennen
  • Epilobium decurrens hort.
  • Epilobium decurrens Rchb.
  • Epilobium dregeanum E.Mey. ex Hausskn.
  • Epilobium dubium Curt.
  • Epilobium dubium Curtis ex With.
  • Epilobium flaccidum Brot.
  • Epilobium glabellum var. tetragonum (L.) Maiden & Betche
  • Epilobium gredillae Sennen & Elias
  • Epilobium gredillae var. glabrum Sennen
  • Epilobium heterophyllum Nutt. ex Hausskn.
  • Epilobium lamyi F.W.Schultz
  • Epilobium lamyi var. pseudoadnatum Tacik

and 28 more.

Sourcesevery claim on this page

  1. World Flora Online Plant List. accepted name, authority, classification. CC0. Retrieved 2026-07-12.
  2. iNaturalist. photographs and flowering annotations, CC0 / CC BY / CC BY-SA only. per photograph. Retrieved 2026-06-27.
  3. Wikidata. common name (P1843), joined on the World Flora Online identifier (P7715). CC0. Retrieved 2026-07-13.
  4. Kew, World Checklist of Vascular Plants (WCVP v16). native distribution by TDWG level-3 botanical country, and life form. CC BY 3.0. Retrieved 2026-06-04.

We publish what we can source and we say so when we cannot. This page has no care advice and no toxicity claim, because we do not yet have those from a source we can cite.