Oenothera biennis, commonly known as the common evening primrose, German rampion, or king's cure-all, is a biennial herbaceous plant in the family Onagraceae. Native to North America, it has been introduced and naturalized across much of Europe and Asia. The genus name Oenothera is derived from the Greek oinos (wine) and ther (hunt or wild beast), a nomenclature that classical botanists likely applied to a plant whose roots were supposedly used to flavor wine or attract game. The species epithet biennis refers to its two-year life cycle: during the first year, the plant grows a low-lying, ground-hugging rosette of leaves, and in the second year, it produces a tall, bolt-upright stalk topped with its iconic yellow flowers. Historically, this plant has been an essential resource in Indigenous North American ethnobotany, serving as both food and medicine for centuries.

The plant is characterized by its dramatic, nocturnal blooming habit; its bright yellow, four-petaled flowers open rapidly in the late afternoon or early evening and typically wither by the following day. These flowers attract long-tongued hawk moths and other nocturnal pollinators with a sweet, lemony fragrance. The stalks can reach heights of up to 1.5 meters and are often tinged with red. Following the flowers, the plant produces elongated, woody capsules filled with numerous small, dark seeds. Oenothera biennis is a quintessential "pioneer species," frequently found colonizing disturbed ground, roadsides, railways, and meadows, where it thrives in open, sunny conditions with well-draining soil.

As a food source, almost every part of Oenothera biennis is edible. The first-year rosettes of leaves can be harvested in early spring and eaten as a potherb, offering a mild, slightly peppery flavor. The fleshy taproots of the first-year plants are particularly prized; when harvested in the fall or early spring, they are succulent and somewhat sweet. Traditionally known as "German rampion," these roots were once a staple cooked vegetable, boiled or roasted to bring out a flavor profile reminiscent of parsnips. While the flowers are used as edible garnishes in modern culinary presentations, the most economically significant food product is the oil extracted from the small, dark seeds.

Nutritionally, the plant is a powerhouse of essential fatty acids. The seeds are exceptionally high in gamma-linolenic acid (GLA), a rare omega-6 fatty acid that serves as a precursor to anti-inflammatory prostaglandins in the human body. The leaves and roots are rich in Vitamin C, calcium, magnesium, and potassium. In traditional folk medicine, the entire plant was used to soothe inflammation, treat skin disorders, and ease respiratory ailments. Modern pharmacological research focuses heavily on evening primrose oil (EPO), which is widely supplemented to manage symptoms of premenstrual syndrome (PMS), rheumatoid arthritis, eczema, and other inflammatory conditions.

Major ingredients derived from this food source include cold-pressed evening primrose seed oil, dried root powders, and wild-harvested spring leaf greens. Significant bioactive compounds associated with the source include gamma-linolenic acid (GLA), linoleic acid, oleic acid, ellagic acid, and various flavonoids such as kaempferol and quercetin derivatives.