Epilobium angustifolium is a plant in the family Onagraceae, native to the temperate regions of the Northern Hemisphere. It goes by several common names: fireweed in North America, great willowherb in parts of Canada, rosebay willowherb in Britain and Ireland. The genus name Epilobium derives from the Greek epi (“upon”) and lobos (“pod”), referring to the position of the flower above the inferior ovary that develops into an elongated capsule. This is complemented by the Latin specific epithet angustifolium (“narrow‑leaved”). The common name fireweed derives from the species’ propensity to colonize burnt sites following forest fires.