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 ==Use by humans==