Oenothera - evening primrose

Oenothera is a genus of about 125 species of annual, biennial and perennial herbaceous flowering plants, native to North and South America. It is the type genus of the family Onagraceae. Common names include evening primrose, suncups, and sundrops.

The species vary in size from small alpine plants 10 cm tall (e.g. O. acaulis from Chile), to vigorous lowland species growing to 3 m (e.g. O. stubbei from Mexico). The leaves form a basal rosette at ground level and spiral up to the flowering stems; the leaves are dentate or deeply lobed (pinnatifid). The flowers open in the evening, hence the name "evening primrose", and are yellow in most species but white, purple, pink or red in a few; there are four petals. One of the most distinctive features of the flower is the stigma with four branches, forming an X shape.

The genus Oenothera may have originated in Mexico and Central America from which it spread into North and South America and, with the advent of international travel, species are now found in most temperate regions. During the Pleistocene era a succession of ice ages swept down across North America, with intervening warm periods. This was repeated for four ice ages, with four separate waves of colonization, each hybridizing with the remnants of the previous waves. This generated a present-day group of species forming the subsection Euoenothera which is very rich in genetic diversity, spread right across the North American continent. These species are morphologically diverse and are largely interfertile and so the species boundaries have been a source of dispute amongst taxonomists.


Cultivation and uses
Young roots can be eaten like a vegetable (with a peppery flavour), or the shoots can be eaten as a salad. The whole plant was used to prepare an infusion with astringent and sedative properties. It was considered to be effective in healing asthmatic coughs, gastro-intestinal disorders, whooping cough and as a sedative pain-killer. Poultices containing O. biennis were at one time used to ease bruises and speed wound healing. One of the common names for Oenothera, "Kings cureall", reflects the wide range of healing powers ascribed to this plant, although it should be noted that its efficacy for these purposes has not been demonstrated in clinical trials.

The mature seeds contain approximately 7-10% gamma-linolenic acid, a rare essential fatty acid. The O. biennis seed oil is used to reduce the pains of premenstrual stress syndrome. Gamma-linolenic acid also shows promise against breast cancer.

Evening Primroses are very popular ornamental plants in gardens. For propagation, the seeds can be sown in situ from late spring to early summer. The plant will grow successfully in fertile soils if competing species are kept at bay. Evening primrose species can be planted in any ordinary, dry, well-drained garden soil (preferly sandy loam) in an open site that is sunny to partly shady. They are fairly drought-resistant.

The first plants to arrive in Europe reached Padua from Virginia in 1614 and were described by the English botanist John Goodyer in 1621. Some species are now also naturalized in parts of Europe and Asia, and can be grown as far north as 65° N in Finland. The UK National Council for the Conservation of Plants and Gardens, based at Wisley, maintains an Oenothera collection as part of its National Collections scheme.


Selected species
Oenothera biennis (Common evening primrose or Evening star) 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.

Oenothera caespitosa, also called Tufted evening primrose, is a perennial plant of the genus Oenothera. Oenothera caespitosa grows to 10 cm (4 in) tall. It is good for rock gardens. The flowers are white and become pink in time.

Oenothera deltoides, also known as Birdcage Primrose or Dune Primrose, is a desert plant with large, white, papery thin flowers. The plant is grayish with basal and deltoid shaped leaves. The flowers turn pinkish as they mature. The plants thrive in desert areas of the Southwestern United States in sandy areas. When the plants die, the stems curl upward and form the "birdcage" for which the common name is derived. This annual plant flowers in April and May in the Mojave and Colorado deserts.

Oenothera elata

Oenothera odorata is a perennial plant belonging to the genus Oenothera and native to South America. Oenothera odorata grows to 60-90 cm (24-36 in) tall. It flowers in summer with yellow flowers which become red in time.

Oenothera rosea, also known as Pink evening primrose or Rose of Mexico, is a plant belonging to the genus Oenothera and native to northern Mexico and USA.

Oenothera speciosa - Pink primrose, also known as Pinkladies and Showy evening primrose, is a herbaceous perennial wildflower native to the southeastern United States and Mexico. The species name speciosa means "showy"

Oenothera stubbei

Oenothera pallida

Oenothera erythrosepala

Oenothera perennis

Oenothera longissima

Oenothera macrocarpa

Oenothera pilosella

Oenothera taraxacoides

Oenothera tetraptera

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