Oenothera biennis

Oenothera biennis (Common evening primrose or Evening star), is a biennial flowering plant growing to 1.2 m (3 to 4 ft), with easy germination. It is also known as Weedy evening-primrose, German rampion, hog weed, King's cure-all, and fever-plant.

Its hermaphrodite, pale yellow flowers bloom for most of the summer, from June to September. They open in the evening, hence the name "evening primrose", and are pollinated by Lepidoptera (Moths and Butterflies) and bees.

The mature seeds contain approximately 7-10% gamma-linolenic acid, a rare essential fatty acid. The O. biennis seed oil is used to reduce the pains of premenstrual stress syndrome and is beneficial to the skin of the face. Also, poultices containing O. biennis were at one time used to ease bruises and speed wound healing.

The flower has an unusual response to ultraviolet light. A brilliantly colored center, invisible in visible light, is boldly apparent under ultraviolet.