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.
The taxonomy of the genus has varied between different botanists, but the modern trend is to include the previously recognised genera Boisduvalia, Chamaenerion (previously Chamerion), Pyrogennema and Zauschneria within Epilobium according to Peter H. Raven, who has extensively studied the willowherbs and merges the other segregate genera into Epilobium. Fringed willowherb (Epilobium 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 are known as fireweeds.
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.
The genus name derives from the Greek words "epi" meaning "upon" and "lobos" meaning "lobe", with reference to position of the petals above the ovary.
A number of Epilobium species with slightly asymmetrical (zygomorphic) magenta flowers and alternate leaves are placed in a Chamaenerion group, and are futher separated by some authorities into a genus Chamerion. However, Chamerion has not been universally accepted.<ref name=TPL>{ { cite web |url=http://www.theplantlist.org/tpl1.1/search?q=Chamerion |title=The Plant List: Chamerion |access-date=22 February 2017}}</ref>
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 Noctuidae Mouse moth (Amphipyra tragopoginis), recorded on several species Small angle shades (Euplexia lucipara), recorded on several species Australian grapevine moth (Phalaenoides glycinae), recorded on fringed willowherb (E. ciliatum) Sphingidae 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