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  Oenothera biennis, commonly known as Evening Primrose, Evening Star or Sun Drop, is a species of Oenothera native to eastern and central North America, from Newfoundland west to Alberta, southeast to Florida, and southwest to Texas, and widely naturalized elsewhere in temperate and subtropical regions. Evening primrose oil is produced from the plant. Oenothera biennis is a biennial which means that is has a life span of two years. It grows 30cm to 150cm tall. The leaves are lanceolate, 5–20cm long and 1–2.5cm broad, produced in a tight rosette the first year, and spirally on a stem the second year.
Blooming lasts from late spring to late summer. The flowers are hermaphrodite, produced on a tall spike and only last until the following noon. They open visibly fast every evening producing an interesting spectacle, hence the name "evening primrose". The blooms are yellow, 2.5–5cm diameter, with four bilobed petals. The flower structure has an invisible to the naked eye bright nectar guide pattern. This pattern is apparent under ultraviolet light and visible to its pollinators, moths, butterflies, and bees. The mature seeds contain approximately 7–10% gamma-linolenic acid, an essential fatty acid. The Oenothera biennis seed oil is used medicinally to reduce the pains of premenstrual stress syndrome and is beneficial to the skin of the face. Also, poultices containing Oenothera biennis were at one time used to ease bruises and speed wound healing. Its leaves and flowers are edible and traditionally were used as a leaf vegetable. The flowers are often used as an ingredient in salads. Evening primrose is sometimes used to treat eczema.
  
  
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