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evening primrose family of flowering plants, belonging to the myrtle order (Myrtales), comprising 21 genera concentrated in the temperate region of the New World. The family is characterized by flowers with parts mostly on the plan of four (four sepals, four petals, four or eight stamens), but there are some exceptions. The ovary is inferior (i.e., below the flower proper). In the temperate zone the family is known from genera such as Epilobium, including the great willow herb, or fireweed (E. angustifolium). Another well-known genus is Oenothera (with about 80 species), which has been of great importance in studies in genetics and evolution.