Evening primrose is a native of North America and was introduced into European botanical gardens in 1614 from Virginia, USA. It has since become a wild plant and is a familiar sight on roadsides, dunes, railway banks and waste places.
It is a biennial plant. In the wild seed germinates in the spring and in the first year the plant forms a rosette of leaves which is flat to the ground and which may grow up to 30 cm across by the autumn. This maximises overwintering survival chances. In the spring of the second (reproductive) year the plant produces a central stem with a variable number of branches; it grows to a height of 20-200 cm. Each stem bears numerous yellow blooms which open in the evening. Flowering normally starts in July and fresh flowers are produced each day for several months. They are self-pollinated but some are cross-pollinated and they can be pollinated by moths.
Although the roots and various parts of the plant can be eaten, the main interest in producing the plant is that the seeds are an excellent source of g-linolenic acid. It also contains tocopherol, tryptophan, sitosterol and vitamin B. g-linolenic acid is an essential fatty acid in human metabolism i.e. it cannot be synthesised in the body and is required by the body for various functions e.g. neurotransmitter synthesis, healthy skin.
Evening primrose oil is also sold as a dietary supplement in health food shops.