Oenothera biennis (common evening primrose, evening star, or sun drop) is a species of Oenothera native to eastern and central North America, from Newfoundland west to Alberta, southeast to Florida, and southwest to Texas, and widely naturalized elsewhere in temperate and subtropical regions. Evening primrose oil is produced from the plant.
Growth and flowering
Oenothera biennis has a life span of two years (biennial) growing to 30–150 cm (12–59 in) tall. The leaves are lanceolate, 5–20 cm (2.0–7.9 in) long and 1–2.5 cm (0.39–0.98 in) broad, produced in a tight rosette the first year, and spirally on a stem the second year.
Blooming lasts from late spring to late summer. The flowers are hermaphrodite, produced on a tall spike and only last until the following noon. They open visibly fast every evening producing an interesting spectacle, hence the name "evening primrose."
The blooms are yellow, 2.5–5 cm (0.98–1.97 in) diameter, with four bilobed petals. The flower structure has an invisible to the naked eye bright nectar guide pattern. This pattern is apparent under ultraviolet light and visible to its pollinators, moths, butterflies, and bees.
The fruit is a capsule 2–4 cm (0.79–1.57 in) long and 4–6 mm (0.16–0.24 in) broad, containing numerous 1–2 mm (0.039–0.079 in) long seeds, released when the capsule splits into four sections at maturity.
Primrose moth (Schinia florida) in flower
It is also known as Weedy evening-primrose, German rampion, hog weed, King's cure-all, and fever-plant.
Cultivation and uses
The mature seeds contain approximately 7–10% gamma-linolenic acid, an essential fatty acid. The O. biennis seed oil is used to reduce the pains of premenstrual stress syndrome and is beneficial to the skin of the face. Also, poultices containing O. biennis were at one time used to ease bruises and speed wound healing.
Evening primrose is sometimes used to treat eczema. Natural Standard has given evening primrose oil a "B" score for the treatment of eczema; meaning there is good scientific evidence supporting its use. The symptoms of eczema can be exacerbated due to scratching and drying out the skin. Evening primrose oil contains linoleic acid, which is the primary oil found in the stratum corneum. Supplementation with EPO may help rehydrate skin that has been scratched due to eczema. Furthermore, gamma-linoleic acid is metabolized into anti-inflammatory compounds, which may contribute to its ability to provide symptomatic relief in eczema. Most studies evaluating the effectiveness of EPO used 4 capsules of standardized extract (~1600 mg of evening primrose oil TOTAL) dosed by mouth twice daily for up to 12 weeks.
Evening Primrose Oil has been shown to slightly reduce blood pressure, can increase clotting time (use with caution if you take warfarin or aspirin), and should not be used by epileptics as it lowers the seizure threshold. Safety has not been evaluated in pregnant or nursing women.
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- Germplasm Resources Information Network: Oenothera biennis
- http://www.umm.edu/altmed/articles/evening-primrose-000242.htm (Retrieved 6/17/13)
- http://nccam.nih.gov/health/eveningprimrose (Retrieved 6/17/13)
- Borealforest: Oenothera biennis
- Plants of British Columbia: Oenothera biennis
- Jepson Flora: Oenothera biennis
- Ultraviolet Flowers: Oenothera biennis
- Blanchan, N. (1922). Wild Flowers Worth Knowing. Project Gutenberg Literary Archive Foundation.
- Gaertner, Erika E. (1968). "Additions to the list of wild edible plants preservable by the deep freeze method". Economic Botany 22 (4): 369. doi:10.1007/BF02908133
- Angelo, Giana. "Essential Fatty Acids and Skin Health." Linus Pauling Institute: Micronutrient Information Center. Oregon State University, Feb. 2012. Web. 30 Nov. 2012.
- Profile: Yellow Evening-primrose (Oenothera biennis) Photos, Drawings, Text. (Wild Plants of Winnipeg from Nature Manitoba)