Evening primrose (Oenothera biennis L.)

The term evening primrose refers to Oenothera biennis L., a biennial herbaceous species native to North America and now naturalised in many temperate regions, where it colonises sandy, well-drained soils, roadsides, fallow fields and disturbed habitats. In its first year, the plant develops a basal rosette of elongated leaves, and in the second year an erect stem bearing inflorescences with characteristic yellow, cup-shaped flowers, which open mainly in the evening hours. As the fruits (elongated capsules) ripen, they produce the seeds, which are the main part of interest.

From a morphological and agronomic standpoint, evening primrose is valued primarily for its seeds, which are harvested when the plant has completed its vegetative cycle. The seeds are separated from the capsules, dried and sent to subsequent processing stages. The extraction process can be carried out by mechanical pressing or by more sophisticated techniques in order to obtain an oil with consistent characteristics. Pedoclimatic conditions, cultivation practices and harvest timing influence both seed yield and the compositional profile of the oil.

The composition of evening primrose relates mainly to the oil contained in the seeds, which is rich in fatty acids, with a significant presence of linoleic acid and γ-linolenic acid (GLA), along with smaller amounts of oleic acid and other lipid fractions. The seeds also provide fibre, proteins, minerals, phenolic compounds and tocopherols with antioxidant function. Levels of essential fatty acids may vary according to growing area, climatic conditions and extraction parameters.

From a technological perspective, evening primrose is used in the food sector (seeds and oil as nutritional ingredients) and for the production of raw materials destined for herbal preparations, dietary supplements and, to a lesser extent, topical formulations. The quality of the raw material depends on correct species identification, harvesting techniques, drying methods and storage conditions, as well as control of extraction parameters and oil standardisation. In all applications, careful management of the seeds and processing steps is essential to preserve fatty acid content and the technological characteristics that distinguish common evening primrose.

Botanical classification (APG IV)

• Botanical name: Oenothera biennis L.

• Common name: common evening primrose, evening primrose

• Family: Onagraceae

• Order: Myrtales

Modern clades (phylogenetic):

• Angiosperms

• Eudicots

• Core eudicots

• Rosids

• Domain: Eukaryota

• Kingdom: Plantae

Cultivation and growth conditions

Climate

Common evening primrose is a biennial herb widespread in temperate and cool–temperate regions. It tolerates winter cold and short frost periods, entering vegetative dormancy during the cold season. It prefers summers that are mild to moderately warm and is penalised by very dry conditions with prolonged heat if no water supply is available.

Exposure

The species grows best in full sun, which promotes compact vegetative growth, abundant flowering, and regular seed set. It can adapt to bright partial shade, but excessive shading reduces development of the basal rosette, the emergence of flowering stems, and overall fruit production.

Soil

Evening primrose is quite adaptable, but performs best in soils that are:

• Well drained, with no prolonged waterlogging;

• Of loam or loam-sandy texture;

• Moderately supplied with organic matter;

• With a slightly acidic to neutral pH.

Soils that remain waterlogged penalise the deep taproot and increase the risk of root rot. Very poor soils slow growth, while balanced fertility supports vigour, flowering, and seed yield.

Irrigation

The crop benefits from a moderately moist soil:

• In the juvenile phase, after germination and during formation of the basal rosette;

• In spring, during stem elongation and flower initiation.

Plants tolerate short dry periods, but regular water availability improves flowering and capsule development. Water should be supplied without excess: persistent saturation and high humidity favour root and collar diseases.

Temperature

The favourable temperature range is roughly 10–24 °C.

• Cool spring temperatures support the onset of flowering.

• Excessively hot, dry conditions may accelerate seed set and shorten the vegetative cycle.

• In the rosette (overwintering) stage, plants tolerate temperatures well below 0 °C.

Fertilization

Nutrient demands are not high, but the species responds well to:

• Organic amendments (mature compost) to improve soil structure and porosity;

• Moderate nitrogen (N) inputs in early stages to support leaf growth;

• Adequate phosphorus (P) and potassium (K) to promote root development, balanced growth, and flowering.

Excess nitrogen favours lush vegetative growth at the expense of flowering and capsule formation.

Crop care

• Sowing and early management: Evening primrose reproduces readily by seed. Young rosettes must be kept free from competitive weeds that reduce light, water, and nutrients.

• Thinning: Useful in seedbeds or dense stands to reduce intraspecific competition and support correct development of the taproot.

• Weed control: Preferably by shallow hoeing and organic mulches.

• Plant health: The species is generally hardy; problems usually arise only under conditions of high humidity and poor drainage, which can favour fungal diseases.

Harvest

In the typical biennial cycle:

• In the first year, the plant forms a basal rosette and develops the root system.

• In the second year, it produces flowering stems and inflorescences, followed by capsules containing numerous small seeds.

Capsules are harvested when they are yellow-brown and close to natural dehiscence. For technical uses or seed production, capsules are dried in ventilated, shaded environments and then threshed to extract the seeds.

Propagation

Propagation is almost exclusively by seed:

• Autumn or spring sowing, either directly in the field or in seedbeds.

• Seeds germinate best in cool, well-worked, light soils.

• Timely thinning allows proper rosette development and reduces competition.

Vegetative propagation is not commonly used, as the biennial life cycle makes natural seeding the simplest and most efficient propagation method.

Indicative nutritional values per 100 g (seeds)

Energy: ~550–590 kcal
Protein: ~20–23 g
Total carbohydrates: ~4–6 g
Dietary fibre: ~10–12 g
Total fat: ~52–55 g

• SFA: minor fraction of total fat

• MUFA

• PUFA (predominant fraction, including linoleic acid and gamma-linolenic acid)
  Minerals: potassium, calcium, magnesium, phosphorus
  Vitamins: vitamin E and small amounts of B-group vitamins
  Sodium: very low

Values may vary with variety, growing conditions and seed maturity.

Key constituents

• Lipid fraction

  • high proportion of polyunsaturated fatty acids (PUFA), mainly linoleic acid (omega-6) and gamma-linolenic acid (GLA)

  • smaller amounts of saturated fats (SFA) and monounsaturated fats (MUFA)

• Minor lipid components

  • tocopherols (vitamin E) contributing to oxidative stability

  • phytosterols and other unsaponifiable compounds

• Non-lipid matrix

  • dietary fibre and plant cell wall polysaccharides

  • vegetable proteins with a balanced, though not complete, amino acid profile

• Micronutrients

  • minerals such as potassium, calcium, magnesium and phosphorus

  • traces of B-group vitamins

Production process

• Cultivation and harvesting

  • field cultivation under temperate conditions

  • harvesting of mature seed capsules when fully developed and dry enough for threshing

• Seed cleaning and drying

  • separation of seeds from plant material

  • cleaning, grading and gentle drying to a safe moisture level

• Oil extraction

  • mechanical cold-pressing or controlled industrial pressing to obtain evening primrose oil

  • in some processes, further extraction and refining may be used to optimise yield

• Filtration and quality control

  • filtration/clarification of crude oil

  • analytical control of fatty-acid profile, acidity, peroxide value and purity

• Packaging

  • filling into dark or light-protected containers to limit oxidation

  • storage and distribution under controlled conditions

Physical properties

Seeds are small, brownish and rich in oil.
The oil is fluid, with a yellow to golden colour and relatively low viscosity.
Due to the high PUFA content, it is sensitive to oxidation if not properly protected from light, oxygen and heat.
At room temperature it remains liquid and shows typical behaviour of a light vegetable oil.

Sensory and technological properties

Mild, slightly nutty and herbal aroma
Delicate, neutral-to-slightly nutty flavour
High spreadability and good skin feel (for cosmetic use)
Technologically, the oil is suitable as:

• a carrier oil in nutritional formulations and supplements

• a functional ingredient in oil blends

• a lipid phase in cosmetic emulsions

Because of the high PUFA content, careful control of oxidation (antioxidants, packaging, storage) is important.

Food applications

• Use in food supplements, typically in soft-gel capsules containing evening primrose oil

• Possible addition in small quantities to salads and cold dishes (where permitted and appropriate)

• Inclusion in blends of vegetable oils designed for specific fatty-acid profiles

• Ingredient in specialised nutritional products, where controlled doses of GLA are desired

Culinary use as a standard cooking oil is limited, especially for high-temperature applications, because of its high PUFA content and oxidation sensitivity.

Nutrition & health

• High energy density, typical of oils and oil-rich seeds

• Significant content of polyunsaturated fatty acids, especially omega-6 (linoleic acid and gamma-linolenic acid)

• Source of vitamin E and phytosterols

• Traditionally positioned as a nutraceutical ingredient in the context of balanced diets and specific formulations

• Its use should be framed within the overall dietary fat balance, considering total PUFA and SFA intake from all sources

Portion note

For food use, evening primrose oil is generally taken in small quantities, typically 1–3 g per day in the form of supplements or as part of carefully formulated products.
The effective portion should follow product-specific recommendations and overall dietary guidance.

Allergens & intolerances

Evening primrose is not among the major regulated food allergens.
Rare individual sensitivities to seed oils are possible.
In commercial formulations (capsules, enriched foods), any potential allergens usually derive from excipients, capsule materials (e.g. gelatine) or other added ingredients and must therefore be checked on the label.

Storage & shelf-life

• Seeds

  • store in a cool, dry place, protected from pests

  • avoid high humidity to prevent mould growth

• Oil

  • store in well-closed, preferably dark containers, away from light, heat and oxygen

  • refrigeration or cool storage can improve stability

  • shelf-life is strongly influenced by protection from oxidation; once opened, it is advisable to consume within a limited time frame

Use of antioxidants (e.g. tocopherols) and oxygen-barrier packaging can help maintain quality.

Safety & regulatory

• Evening primrose seeds and oil must comply with general food safety and hygiene requirements, including application of HACCP in production and packing.

• Controls include checks for contaminants, residues, oxidation markers and compliance with specifications for composition and purity.

• Products marketed as food supplements must comply with specific regulations on composition, labelling, recommended daily dose and health/ nutrition claims, depending on the jurisdiction.

Labelling

For evening primrose oil and seed-based products, the label should indicate:

• the botanical source and part used (e.g. “evening primrose oil from Oenothera biennis seeds”)

• full ingredient list for blends or compound products

• net content, batch number, best-before/use-by date

• storage conditions

• for supplements, the recommended daily dose and any required warnings

• clear highlighting of any allergens originating from other ingredients

Troubleshooting

• Rancid or off-odour oil

  • causes: oxidation due to exposure to light, heat or air

  • actions: improve packaging, use dark bottles, reduce storage temperature, limit storage time after opening

• Low extraction yield

  • causes: immature seeds, poor seed quality or suboptimal pressing conditions

  • actions: optimise harvest timing, drying, pressing parameters and pre-treatments

• Hazy or discoloured oil

  • causes: incomplete filtration, oxidation, or storage at low temperatures causing temporary cloudiness

  • actions: refine or filter as appropriate, verify storage conditions, evaluate oxidative stability

Sustainability & supply chain

• Evening primrose can be integrated into crop rotations with relatively low input requirements, contributing to soil management and diversification.

• Seed production with good agricultural practices supports sustainable use of land and resources.

• A traceable supply chain, with clear information on origin, cultivation and processing, is important for quality assurance and market positioning.

• Efficient extraction, careful handling and reduced waste along the chain help minimise environmental impact.

Main INCI functions (cosmetics)

In cosmetics, evening primrose is commonly listed as:

• Oenothera Biennis Oil

Typical cosmetic functions:

• emollient oil in skin-care emulsions and body oils

• conditioning and softening effect for skin and hair

• functional component in products positioned as containing omega-6 or “nutritive” plant oils

Cosmetic use requires that the oil meets standards for purity, stability (particularly of PUFA) and safety as defined by cosmetic regulations.

Conclusion

Common evening primrose (Oenothera biennis L.) is a seed-oil plant of notable interest due to its content of polyunsaturated fatty acids, especially gamma-linolenic acid, together with tocopherols, phytosterols and a fibrous seed matrix. The oil is used mainly in food supplements and cosmetic products, where it acts as a functional lipid component and carrier.
Appropriate agricultural practices, rigorous quality control and proper storage conditions are essential to preserve the nutritional and technological properties of the oil and to guarantee its safety and reliability in both food and cosmetic applications.

Mini-glossary

• SFA – saturated fatty acids; fats with no double bonds. Excessive replacement of other fats by SFA may be less favourable for blood lipid profiles.

• MUFA – monounsaturated fatty acids; fats with one double bond, generally preferable to high SFA intake within a balanced diet.

• PUFA – polyunsaturated fatty acids; fats with two or more double bonds, including omega-3 and omega-6 families that contribute to many physiological processes.

• HACCP – Hazard Analysis and Critical Control Points; systematic approach to identifying and controlling food-safety hazards throughout the production chain.

Studies

Evening primrose produces a seed oil whose active ingredients are triglycerides of fatty acids, mainly linolenic and gamma linolenic. (1).

Evening primrose oil is administered internally in the treatment and mitigation of the symptoms of atopic dermatitis. A clinical study in patients with atopic dermatitis, in which the influence of Evening primrose oil was estimated on inflammation, dryness, exfoliation and itching, revealed an improvement in all parameters compared to the placebo group (2).

Evening primrose oil should be used with caution in patients with epilepsy and schizophrenia or by people taking epilectic drugs. It should not be given during pregnancy or breastfeeding or to children without medical supervision (3).

Essential oil exerts an antioxidant action.

Evening primrose polyphenol extract demonstrated anti-migrant, anti-invasive and antimetastatic potential towards prostate and breast cancer cell lines (4).

In this study, evening primrose was shown to promote the contraction of matrix collagen, actin polymerisation and the production of essential ECM proteins. These results confirm the therapeutic value of this plant in slowing down the progression of skin ageing (5).

Evening primrose studies

References_____________________________________________

(1) WHO. Oleum Oenotherae Biennis. Geneva: World Health Organization; 2002. Monographs on selected medicinal plants; pp. 217–30.

(2) Pytkowska K. Effect of lipids on epidermal barrier function. Wiadomości PTK. 2003;2:7–10.

(3) WHO. Oleum Oenotherae Biennis. Geneva: World Health Organization; 2002. Monographs on selected medicinal plants; pp. 217–30.

(4) Lewandowska U, Owczarek K, Szewczyk K, Podsędek A, Koziołkiewicz M, Hrabec E. Influence of polyphenol extract from evening primrose (Oenothera paradoxa) seeds on human prostate and breast cancer cell lines.   Postepy Hig Med Dosw (Online). 2014 Feb 3;68:110-8. doi: 10.5604/17322693.1088036.

Abstract. There is growing interest in plant polyphenols which exhibit pleiotropic biological activities, including anti-inflammatory, antioxidant, and anticancer effects. The objective of our study was to evaluate the influence of an evening primrose extract (EPE) from defatted seeds on viability and invasiveness of three human cell lines: PNT1A (normal prostate cells), DU145 (prostate cancer cells) and MDA-MB-231 (breast cancer cells). The results revealed that after 72 h of incubation the tested extract reduced the viability of DU 145 and MDA-MB-231 with IC50 equal to 14.5 μg/mL for both cell lines. In contrast, EPE did not inhibit the viability of normal prostate cells. Furthermore, EPE reduced PNT1A and MDA-MB-231 cell invasiveness; at the concentration of 21.75 μg/mL the suppression of invasion reached 92% and 47%, respectively (versus control). Additionally, zymographic analysis revealed that after 48 h of incubation EPE inhibited metalloproteinase-2 (MMP-2) and metalloproteinase-9 (MMP-9) activities in a dose-dependent manner. For PNT1A the activities of MMP-2 and MMP-9 decreased 4- and 2-fold, respectively, at EPE concentration of 29 μg/mL. In the case of MDA-MB-231 and DU 145 the decrease in MMP-9 activity at EPE concentration of 29 μg/mL was 5.5-fold and almost 1.9-fold, respectively. In conclusion, this study suggests that EPE may exhibit antimigratory, anti-invasive and antimetastatic potential towards prostate and breast cancer cell lines.

(5) Ceccacci S, De Lucia A, Tito A, Tortora A, Falanga D, Arciello S, Ausanio G, Di Cicco C, Monti MC, Apone F. An Oenothera biennis Cell Cultures Extract Endowed with Skin Anti-Ageing Activity Improves Cell Mechanical Properties. Metabolites. 2021 Aug 9;11(8):527. doi: 10.3390/metabo11080527.

Abstract. Skin aging is a very well-known process setting a gradual worsening of skin mechanical features due to a decline in the production of the extra-cellular matrix machinery and to a concurrent change in the contraction process. To slow this progression, it is crucial to induce the expression of several proteins able to promote elastic fibers formation and tissue repair. Here, the Oenothera biennis cell culture aqueous extract has been investigated from a chemical point of view and then it was tested in vitro, in cell, and in ex vivo experiments as adjuvant in counteracting skin aging. Accordingly, it has been shown that the Oenothera biennis extract was able, by increasing MYLK gene expression, to promote matrix collagen contraction, actin polymerization, and the production of essential ECM proteins.