General: erect, simple or branched biennial or short-lived perennial, from stout taproot. Stems 30-100 cm tall, usually grayish with flat, stiff hairs and with a mixture of longer hairs, spreading, reddish-based, and with expanded bases.
Leaves: in basal rosettes 1st year, and alternate 2nd year. Lower leaves stalked, the upper ones almost stalkless, lanceolate, the largest ones up to 10-15 cm long and 1-2.5 cm broad, entire to wavy-toothed.
Flowers: bright yellow, with 4 petals 1-2 cm long. Several flowers in a single, long dense cluster, blooming mostly in the evening, the buds erect. Sepals bent backward, 10-15 mm long, their free tips 1-3 mm. long in the bud. Bracts from shorter to longer than the mature pods. Hypanthium free, 3-5 cm long. Stamens almost equal to the petals and style, the anthers 4-6 mm long. Stigma lobes linear, 4-7 mm long.
Fruits: pods, 25-40 mm long, erect, hairy, ellipsoid. Seeds numerous, not hair-tufted.
Chiefly in meadows and along stream banks, from the plains to the lower mountains, in w. and c. parts of MT. Also throughout most of the n.w. to e. U.S.
The root of evening primrose is edible cooked. It can be boiled and eaten like salsify. It is fleshy, sweet and succulent, and is said to be wholesome and nutritious. A peppery taste, the taste somewhat resembles salsify or parsnips. Young shoots can be eaten raw or cooked. Mucilaginous, with a peppery flavor, they are best used sparingly. Flowers have a sweet taste and has been used in salads or as a garnish. Young seedpods can be cooked or steamed. The seed contains 28% of a drying oil. It is edible and a very good source of gamma-linolenic acid, an essential fatty acid that is not found in many plant sources and has numerous vital functions in the body. The seed, however, is very small and difficult to harvest, it has to be done by hand. Overall yields are low, making the oil very expensive to produce.
The bark and the leaves are astringent and sedative. They have proved of use in the treatment of gastro-intestinal disorders of a functional origin, whooping cough and asthma. A syrup made from the flowers is also an effective treatment for whooping cough. The bark is stripped from the flowering stem and dried for later use, the leaves are also harvested and dried at this time. Evening primrose oil has become a well-known food supplement since the 1980's. Research suggests that the oil is potentially very valuable in the treatment of multiple sclerosis, pre-menstrual tension, hyperactivity etc. It is also taken internally in the treatment of eczema, acne, brittle nails, rheumatoid arthritis and alcohol-related liver damage. Regular consumption of the oil helps to reduce blood cholesterol levels and lower the blood pressure. The seed is a good source of gamma-linolenic acid, an unsaturated fatty acid which assists the production of hormone-like substances. This process is commonly blocked in the body, causing disorders that affect the uterine muscles, nervous system and metabolism. The poulticed root can be applied to piles and bruises. A tea made from the roots is used in the treatment of obesity and bowel pains.
The oil from the seed is added to skin preparations and cosmetics. It is often combined with vitamin E to prevent oxidation. A yellow dye can be obtained from the flowers. A finely ground powder made from the flowering stems is used cosmetically in face-masks to counteract reddened skins.