The taxonomy of the genus has varied between different botanists, but the modern trend is to include the previously recognised genera Boisduvalia, Pyrogennema and Zauschneria within Epilobium. Chamaenerion, previously (Chamerion), is considered distinct, however, 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.
Most species are known by the common name willowherbs for their willow-like leaves. Those that were once separated in Boisduvalia are called spike-primroses or boisduvalias. Those Epilobium species previously placed in the Chamaenerion group and known as fireweeds are now segregated into the genus Chamaenerion.
Fireweed epilobium angustifolium
Description
Epilobiums are mostly herbaceous plants, either annual or perennial; a few are subshrubs. The leaves are opposite or rarely whorled, simple and ovate to lanceolate in shape. The flowers are actinomorphic (radially symmetrical) with four petals that may be notched. These are usually smallish and pink in most species, but red, orange or yellow in a few. 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.
A number of Epilobium species with slightly asymmetrical (zygomorphic) magenta flowers and alternate leaves were placed in a Chamaenerion group, and have been separated by some authorities into the genus Chamerion. However, Chamerion has not been universally accepted and there is now emerging consensus that this group of species should be segregated into the genus Chamaenerion.
Habitat and ecology
Willowherbs sensu lato are typically very quick to carpet large swathes of ground and may become key or dominant species of local ecosystems. In the United Kingdom, for example, rosebay willowherb (Chamaenerion angustifolium) is widely found on mesotrophic soils dominated by false oat-grass (Arrhenatherum elatius), cock's-foot grass (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 also 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). 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: Geometridae
Grey pug (Eupithecia subfuscata), recorded on several species
Elephant hawk-moth (Deilephila elpenor), recorded on several species
Small elephant hawk-moth (Deilephila porcellus), recorded on several species
White-lined sphinx (Hyles lineata), recorded on several species
Use by humans
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.
The National Museum of Natural History recognizes an intermediate number of about 197 species in 10 sections, and consider the former section Chamaenerion (=Chamerion), as a distinct genus. Other sources may list one or two dozen species, more or less:
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.
