Oenothera

Oenothera is a genus of flowering plants in the family Onagraceae, commonly known as evening primroses. It comprises about 125 species native to the Americas, though several have been introduced elsewhere. The plants are typically herbaceous perennials or biennials, with simple, alternate leaves and tall flowering stems.

The flowers are four-petaled and often yellow, opening in the late afternoon or at dusk, which gives rise to the common name. They are produced in elongated inflorescences and are adapted for pollination by moths and bees. After flowering, the plants produce slender, elongated seed capsules containing numerous small seeds. Growth form ranges from low rosettes to upright, branching clumps, depending on species and habitat.

Distribution and habitat vary by species, but Oenothera is commonly found in open, sunny areas such as fields, meadows, roadsides, and disturbed ground. Several species have become naturalized beyond their native range, with Oenothera biennis (common evening primrose) being the most widespread and sometimes considered weedy outside its native North American range.

Taxonomy and genetics have historically been notable for this genus. Oenothera played a role in early 20th-century genetics research, where observations of rapid, stable new phenotypes contributed to debates about mutation theory, though later work clarified the genetic mechanisms involved.

Uses and significance include ornamental horticulture and the production of evening primrose oil from seeds, which is used as a dietary supplement and in traditional remedies.