Oenothera biennis is a plant native to eastern and central North America and widely naturalized elsewhere in temperate and subtropical regions. It has a life span of two years, growing to 30–150 cm (10–60 in) tall. The flowers are yellow and only last until the following noon after blooming. They open visibly fast every evening producing an interesting spectacle, hence the common name "evening primrose."Photograph: George Chernilevsky