Epilobiums are mostly herbaceous plants, either annual or perennial; a few are subshrubs. The leaves are opposite or rarely whorled,[5]: 354 simple and ovate to lanceolate in shape. The flowers are actinomorphic (radially symmetrical) with four petals that may be notched.[5][6] 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.[7]
A number of Epilobium species with slightly asymmetrical (zygomorphic) magenta flowers and alternate leaves were placed in a Chamaenerion group, and have been separated by some authorities into the genus Chamerion. However, Chamerion has not been universally accepted[8] and there is now emerging consensus that this group of species should be segregated into the genus Chamaenerion.[9][1
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