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Epilobium hirsutum 04 ies.jpg
Epilobium hirsutum (great willowherb)
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Myrtales
Family: Onagraceae
Genus: Epilobium

160-200, see text


Chamerion (but see text)

Epilobium is a genus in the family Onagraceae, containing about 160-200 species of flowering plants with a worldwide distribution. They are generally abundant in the subarctic, temperate and subantarctic regions, whereas in the subtropics and tropics they are restricted to the cool montane biomes, such as the New Guinea Highlands where they are plentiful.

The taxonomy of the genus has varied between different botanists, but the modern trend is to include the previously recognised genera Boisduvalia, Chamaenerion, Chamerion, Pyrogennema and Zauschneria within Epilobium. Chamerion might be distinct, however,[1] according to Peter H. Raven, who has extensively studied the willowherbs and merges the other segregate genera into Epilobium. Fringed willowherb (E. ciliatum) is likely a cryptic species complex; apparently these plants also commonly hybridize with their congeners.[2]

Most species are known by the common name willowherbs for their willow-like leaves.[3] Those that were once separated in Boisduvalia are called spike-primroses or boisduvalias. Yet other species, namely those in the Chamerion group, are also known as fireweeds.

Description and ecology[edit]

Ripe capsule of Epilobium canum (zauschneria) releasing seed

They are mostly herbaceous plants, either annual or perennial; a few are subshrubs. The leaves are mostly opposite or whorled, alternate in a few species, simple, and ovate to lanceolate in shape. The flowers have four petals often notched.[4] These are usually smallish and pink in most species, but red, orange or yellow in a few, and large and bright magenta in the Chamerion group. The fruit is a slender cylindrical capsule containing numerous seeds embedded in fine, soft silky fluff which disperses the seeds very effectively in the wind.

Willowherbs are typically very quick to carpet large swathes of ground and may become key or dominant species of local ecosystems. In and around the United Kingdom, for example, rosebay willowherb (E. angustifolium) is widely found in mesotrophic grassland dominated by false oat-grass (Arrhenatherum elatius), cock's-foot (Dactylis glomerata), and red fescue (Festuca rubra), while great willowherb (Epilobium hirsutum) is found in mesotrophic grassland with stinging nettle (Urtica dioica). These two willowherb species are also seen to dominate open habitat early in ecological succession, to the virtual exclusion of other plant life. Broad-leaved willowherb (Epilobium montanum) is found characteristically, though not abundantly, in the mesotrophic grasslands with meadowsweet (Filipendula ulmaria) and sometimes the uncommon Greek valerian (Polemonium caeruleum), which are peculiar to the Pennines. Most willowherbs will not tolerate shade trees and thus are limited to more recently disturbed patches, yielding to other plants over time. Consequently, though the genus contains many pioneer plants, rather few of them are invasive weeds of major importance.

Epilobium species are used as food plants by the caterpillars of certain Lepidoptera species, including:



Use by humans[edit]

Fireweed (E. angustifolium) growing along rail tracks in Denali National Park, Alaska

The main use of Epilobium by humans is as a herbal supplement in the treatment of prostate, bladder (incontinence) and hormone disorders. Many of the small willowherb species are nuisance weeds in gardens. Though few are regularly used as ornamental plants, the larger willowherbs may be attractive in ruderal locales. One of the most frequently recognized members of the genus is the circumboreal fireweed (E. angustifolium), known as rosebay willowherb in the United Kingdom. It rapidly colonizes burnt ground; during the bombing of London in World War II many of the derelict bomb sites were soon covered with these plants, bringing a splash of colour to what was otherwise a very grim scene. It is the floral emblem of Yukon in Canada, Hedmark in Norway (where it is called geitrams) and Southern Ostrobothnia in Finland.

Fireweed is used as a sweetener in northwestern North America. It is put in candy, jellies, ice cream, syrup, and sxusem ("Indian ice cream"). In the late summer its flowers yield pollen and copious nectar which give a rich spicy honey. Its young leaves, roots, and shoots are edible (if somewhat bitter), and rich in provitamin A and vitamin C. The Dena’ina found them also useful as food supplement for dogs and applied sap from the stem to wounds, believing it to have antiinflammatory properties.

Several researchers have studied this taxon. Heinrich Carl Haussknecht in the late 19th century and Peter H. Raven about a century later researched the phylogeny, systematics, and taxonomy of willowherbs. Peter Michaelis' studies of this genus paved the way for understanding of extranuclear inheritance in plants.


The National Museum of Natural History recognizes an intermediate number of about 175 species in 10 sections, including two sections of Chamerion, which they consider distinct.[1] Other sources may list one or two dozen species, more or less:

Epilobium brachycarpum (tall willowherb)
Epilobium canum (zauschneria)

Section Boisduvalia

Section Cordylophorum

Subsection Nuttalia
Subsection Petrolobium

Section Crossostigma

Section Epilobiopsis

Section Macrocarpa

Section Xerolobium

Section Zauschneria

Top left: Epilobium alsinifolium (chickweed willowherb)
Bottom left: Epilobium anagallidifolium (alpine willowherb)
Center: Epilobium tetragonum (square-stemmed willowherb)
Left: Epilobium roseum (pale willowherb)

Right: Epilobium obscurum (dwarf willowherb)]]

Epilobium parviflorum (small-flowered willowherb)

Section Epilobium

Chamerion group[edit]

Section Chamerion

Section Rosmarinifolium

Formerly placed here[edit]

It is possible to distinguish between leaves of different Epilobium species using high-accuracy FT-IR method based on attenuated total reflection (ATR) without time-consuming preparation.[6]


  1. ^ a b Wagner & Hoch [2009a,b]
  2. ^ Bleeker et al. (2007)
  3. ^ "willow-herb". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005.  (Subscription or UK public library membership required.)
  4. ^ Webb,D.A., Parnell, J. and Doogue, D. 1996. An Irish Flora. Dundaldan Press (W. Tempest) Ltd, Dundalk. ISBN 0-85221-131-7
  5. ^ Epilobium pygmaeum. USDA PLANTS.
  6. ^ Krajšek, S., Buh, P., Zega, A., Kreft, S. (2008). Identification of Herbarium Whole-Leaf Samples of Epilobium Species by ATR-IR Spectroscopy. Chemistry & Biodiversity, 5:310-317 http://onlinelibrary.wiley.com/doi/10.1002/cbdv.200890028/abstract;jsessionid=46F30B7C6B30DADFBD57A4789993E047.f01t02


  • Bleeker, Walter; Schmitz, Ulf & Ristow, Michael (2007): Interspecific hybridisation between alien and native plant species in Germany and its consequences for native biodiversity. Biological Conservation 137(2): 248-253. doi:10.1016/j.biocon.2007.02.004 (HTML abstract, appendix reserved for subscribers)
  • Steenkamp, V; Gouws, M.C; Gulumian, M; Elgorashi, E.E. & van Stade, J. (2006): Studies on antibacterial, anti-inflammatory and antioxidant activity of herbal remedies used in the treatment of benign prostatic hyperplasia and prostatitis. Journal of Ethnopharmacology 103(1): 71-75. doi:10.1016/j.jep.2005.07.007 PDF fulltext
  • Wagner, W.L. & Hoch, P.C. [2009a]: Evening Primrose Family website – Chamerion. Retrieved 2009-JAN-26.
  • Wagner, W.L. & Hoch, P.C. [2009b]: Evening Primrose Family website – Epilobium. Retrieved 2009-JAN-26.