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Evening Primrose (Oenothera biennis)
Materia Medica
Family: Onagraceae
Common names: Evening Primrose, Night Willow-Herb, King's Cure-All, Fever Plant, Sundrop
Part used: Seed (for oil); historically root, leaf, flower, and whole plant
Growth habit: Biennial wildflower; first-year rosette, second-year tall flowering stalk
Primary tradition: North American Indigenous use; later European folk and modern seed-oil use
Actions & Energetics
The whole plant has been regarded as nutritive, demulcent, and vulnerary. The seed oil is used for its gamma-linolenic acid (GLA) content, which participates in prostaglandin pathways. Traditional energetics are mild and food-like rather than strongly heating or cooling.
Botanical Description
Oenothera biennis is a native North American biennial. In the first year it forms a basal rosette of leaves. In the second year it sends up a sturdy flowering stalk bearing large, four-petaled yellow flowers that often open in the evening or late day and attract night-flying moths as well as bees. Seeds form in elongated capsules. The plant thrives in disturbed ground, roadsides, and open areas and has naturalized widely.
Traditional Indications
Several North American nations (including Cherokee, Iroquois, Ojibwe, and Potawatomi) used the roots as food (boiled like potatoes), young shoots and leaves as greens, and the plant in poultices for bruises, boils, and hemorrhoids. Teas of the root or plant were used for digestive support and menstrual or bowel discomfort. European herbalists later called it King’s Cure-All and employed it for wounds, coughs, and general restorative purposes. Modern commercial use centers almost entirely on the pressed seed oil rather than the whole plant.
Preparations & Dosage
Whole-Plant Uses (Historical)
Root cooked as a vegetable. Young leaves and shoots eaten as greens. Poultices of root or whole plant applied externally. Infusions of aerial parts for internal traditional use.
Seed Oil
Evening primrose oil is pressed from the seeds and standardized or characterized by its GLA content (typically 8–14%). It is taken as a dietary supplement, commonly in capsule form. Published study doses for various conditions have ranged from roughly 2–8 g of oil daily depending on the trial and indication. Whole-plant preparations and seed oil are chemically different and should not be treated as interchangeable.
Constituents
Seed oil is rich in linoleic acid and gamma-linolenic acid (GLA). The plant also contains mucilage, phenolic compounds, and other constituents typical of the Onagraceae. GLA is the constituent that has driven most modern research interest.
Modern Research
Evening primrose oil has been studied for atopic eczema, cyclical breast pain (mastalgia), premenstrual symptoms, rheumatoid arthritis, diabetic neuropathy, and other conditions. Results are mixed; some trials and reviews show benefit for specific indications while others do not. The oil is one of the better-documented plant sources of GLA. Research on the whole plant is far more limited than research on the oil.
History, Folklore & Spiritual Use
The name King’s Cure-All reflects its former European folk reputation as a broad remedy. Indigenous North American use treated it as both food and medicine. The evening opening of the flowers has given it a gentle nocturnal folklore association, though it is not a strongly “magical” plant in classical Western herbal tradition. Its modern identity is largely tied to the seed oil and GLA research that began in the twentieth century.
Materia Medica Summary
Evening Primrose (Oenothera biennis) is a North American biennial whose roots, leaves, and flowers have a history of food and medicinal use among Indigenous nations and later European folk practice. Modern commerce focuses on the seed oil, valued for its gamma-linolenic acid content. The whole plant and the oil are distinct preparations. Traditional use as a nutritive and vulnerary plant sits alongside contemporary research on the oil for skin, menstrual, and inflammatory concerns.