Epilobium - Description and Ecology

Description and Ecology

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. 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 form key or even dominant species of local ecosystem. 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 Festuce (Festuca rubra), while Great Willowherb (Epilobium hirsutum) is found in mesotrophic grassland with abundant False Oat-grass, Cock's-foot and 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 rich in False Oat-grass, Meadowsweet (Filipendula ulmaria), and sometimes the otherwise rare Greek Valerian (Polemonium caeruleum), which are peculiar to the Pennines. Most willowherbs will not tolerate shade trees well and thus are limited to comparatively freshly disturbed patches, yielding to other plants as the years pass by. 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
• Double-striped Pug (Gymnoscelis rufifasciata), recorded on Fireweed (E. angustifolium)

Noctuidae

• Mouse Moth (Amphipyra tragopoginis), recorded on several species
• Small Angle Shades (Euplexia lucipara), recorded on several species
• The Gothic (Naenia typica), recorded on Fireweed (E. angustifolium)
• Hebrew Character (Orthosia gothica), recorded on Fireweed (E. angustifolium)
• Australian Grapevine Moth (Phalaenoides glycinae), recorded on Fringed Willowherb (E. ciliatum)
• Setaceous Hebrew Character (Xestia c-nigrum), recorded on Fireweed (E. angustifolium)

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