Evening primrose (Oenothera spp.) seed contains ca. 15% protein, 24% oil, and 43% cellulose plus lignin. The protein is unusually rich in sulphur-containing amino acids and in tryptophan. The component fatty acids of the oil are 65–80% linoleic and 7–14% ofγ-linolenic, but noα-linolenic acid.
The 1.5–2% unsaponifiable matter has a composition very similar to that of cottonseed oil. The sterol fraction contains 90%β-sitosterol and the 4-methyl sterol fraction contains 48% citrostadienol;γ-tocopherol dominates its class, with someα- but no other tocopherols.