[2][3] Members of the genus may be called willowherbs (along with Epilobium),[4] or fireweeds,[2] based on a common name used for C. angustifolium.

They are upright herbaceous perennials, growing from a woody base or from rhizomes, with racemes of usually purple to pink flowers.

Although pre-Linnaean authors had used the name Chamaenerion, which may have originated as early as 1561, in 1753 Carl Linnaeus preferred Epilobium.

[5] Some authors continued to use Chamaenerion (or the alternative spelling Chamaenerium), but this name was not published legitimately under the International Code of Nomenclature for algae, fungi, and plants (ICN) until Jean-François Séguier did so in 1754.

[1] It was assumed by some later authors that Séguier's name was a superfluous replacement for Linnaeus' Epilobium,[6] but Sennikov argues that a strict application of the ICN shows that it was legitimate.

[1] Sennikov's conclusion has been accepted by many sources since the publication of his paper, including Tropicos,[7] GRIN Taxonomy for Plants,[4] the Onagraceae website of the Smithsonian Museum of Natural History,[3] and the Global Biodiversity Information Facility.

[8] Some sources published earlier that also split up Epilobium use the name Chamerion, including the Flora of China.

Chamaenerion can be distinguished from Epilobium by features which include: having leaves mostly spirally arranged rather than mostly opposite; having flowers that are zygomorphic rather than mainly radially symmetrical; and lacking a floral tube and a notch in the petals.

[9] Its American name, fireweed, reflects its regular occurrence in areas recovering from wildfires, to which it may be adapted.