T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Oenothera biennis (Common Evening Primrose)

Kingdom: Plantae
Division: Magnoliophyta
(Unranked): Eudicots
Order: Myrtales
Family: Onagraceae
Genus: Oenothera
Species: O. biennis
Binomial name: Oenothera biennis
Common names: Common Evening Primrose, Evening star, Weedy evening-primrose, German rampion, hog weed, King's cure-all, and fever-plant.

Oenothera biennis is a species of Oenothera native to eastern and central North America. The genus is actually related to willowherbs and not to primroses (Primula). Evening primrose tolerates poor soil quality well and is a popular cultivated plant. It also grows wild along riverbanks and in sandy places.
It is a biennial flowering plant growing to 30–150 cm tall. The leaves are lanceolate, 5–20 cm long and 1–2.5 cm broad, produced in a tight rosette in the first year and spirally on the stem in the second year. The flowers are pale yellow, 2.5–5 cm diameter, with four petals; they are hermaphrodite and are produced on a tall spike from late spring to late summer. 
They open in the evening, hence the name "evening primrose", and close by the following noon. The flower has a bright nectar guide pattern, invisible in visible light, but apparent under ultraviolet light, which assists its pollinators: Lepidoptera (moths and butterflies) and bees. 
The fruit is a capsule 2–4 cm long and 4–6 mm broad, containing numerous 1–2 mm long seeds, released when the capsule splits into four sections at maturity.

Evening primrose seeds are simply cold-pressed to obtain their oil. This 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.
The roots of evening primrose were once used as an appetizer to provoke a taste for wine, just as we might eat olives today. The root of evening primrose was a staple of the Native American diet; it was boiled and eaten like a potato and is said to taste of peppery parsnips.

Opened Oenothera biennis flowers. They close at night.

An opening flower.

The upper leaves.

The lower leaves.

Thanks to Wikipedia for text and information http://creativecommons.org/licenses/by-sa/3.0/