Click on the image below to download my paper on evening primrose crops.

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Selected additional papers:

• Fieldsend, A.F. (2007): The influence of oil content on the equilibrium moisture content of evening primrose (Oenothera spp.) seeds. Acta Agronomica Hungarica 55 (4), 485-489. (Short communication).

• O’Connell, M.N., Kethees Wararajah, V., Fieldsend A.F. and Cullum F.J. (2005): Sources of infection and meth- ods of control of Septoria oenotherae in evening primrose (Oenothera spp.) Acta Agronomica Hungarica 53 (4), 385-391.

• Fieldsend, A.F. (2005): Interactive effects of light, temperature and cultivar on photosynthesis in evening primrose (Oenothera spp.) crops. Acta Agronomica Hungarica 52 (4), 333-342.

• Fieldsend, A.F. (1996): Factories in the Field. Green Futures 2, 20-21.

• Fieldsend, A.F. (1996): Evening primrose - from garden flower to oilseed crop. The Horticulturist 5 (3), 2-5.


This site © Andrew Fieldsend 2014. . Feel free to spread all information, but remember to mention your source. Every effort has been made to ensure accuracy but no liability can be accepted for errors or omissions or for the content of external sites.

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A Brief History of Evening Primrose

Evening primrose (Oenothera spp.) has in recent years made the transition from being a wild flower and cottage garden plant to an established agricultural crop. Its value lies in the seed oil which contains at maturity approximately 7-10 per cent γ-linolenic acid, an essential fatty acid with proven value as a nutrient and pharmaceutical in humans. These days, most people know of evening primrose oil, but few will be familiar with the history of the plant, from its origins, through its early use as a folk medicine and as a genetic curiosity stimulating much study, to its commercialisation and development as a crop plant.

Origins and natural distribution

Evening primrose originated in Mexico and Central America some 70 000 years ago. During the Pleistocene era a succession of ice ages swept down across North America, with intervening warm periods. At the end of these ice ages, the primitive evening primroses followed the retreating glaciers, taking advantage of the disturbed ground which they left in their wake, and in this way colonised much of the continent. During the next ice age, most of these colonies were wiped out but, as the ice moved northwards again, so a second wave of evening primroses from Mexico moved with them and recolonised the area. In the process, they encountered and hybridised with the remnants of the first wave. This was repeated for four ice ages, with four separate waves of colonisation, each hybridising with the remnants of the previous waves. This generated a present day population which is enormously rich in genetic diversity, spread right across the North American continent. The process did not stop there, however, since when trade started with Europe, seeds of evening primrose were inadvertently carried with the soil used to ballast the ships returning to Europe. On reaching port, the soil was dumped and colonies of evening primrose became established around the major ports. In this way, plants from different parts of North America were brought together and were able to hybridise to form yet more new plant types and a whole new, diverse population. Evening primrose is now widely naturalised throughout most of Europe and in several other temperate areas.

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In the wild, evening primrose acts as a primary coloniser, springing up wherever a patch of bare, undisturbed ground may be found. This means that it tends to be found in poorer environments such as dunes, roadsides, railway embankments and wasteland. It often occurs as a casual, eventually being out-competed by other species. However the plant will grow successfully in fertile soils (such as gardens) if competing species are kept at bay.

Taxonomy

Evening primrose is a member of the family Onagraceae. Other members of the family include Epilobium - the willow herbs, and the garden plants Clarkia, Godetia and Fuchsia. Taxonomists disagree strongly on the treatment of the genus Oenothera, and the number of recognised species depends on whether the classifier is a ‘splitter’ or a ’lumper’. The former would point to the large number of naturally occurring genetically distinct, uniform, true breeding populations to support their view. Being normally self-pollinated, these are more or less effectively isolated from one another. The latter argue that since crosses between many of these ‘species’ result in fertile progeny, differentiation between these ‘species’ is not justified.

R.E. Cleland, who conducted many studies on the genus Oenothera, subsection Euoenothera, concluded that these plants "do not lend themselves, on the whole, to satisfactory taxonomic treatment". All cultivars in agricultural production are drawn from the subsection Euoenothera and for this reason agricultural evening primroses are normally described simply as Oenothera spp. Most wild evening primrose populations in Britain also belong to this subsection.

It should be noted that evening primrose is quite unrelated to the common primrose, Primula vulgaris.

Traditional uses of the plant

Evening primrose root has been used as a vegetable with a peppery flavour. American Indians consumed the leaves, shoots, roots and seed pods as food, and made extracts for medicinal purposes. 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 evening primrose were 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.

Evening primrose as a garden flower

More recently, evening primrose has gained some popularity as a garden flower. The first to arrive in Europe, common evening primrose (O. biennis) reached Padua from Virginia in 1619 and was described by the English botanist John Goodyer in 1621. Now naturalised in several parts of Britain, it is a prolific seeder and was described as ’a troublesome weed’ as long ago as the eighteenth century. O. biennis and O. erythrosepala (syn. O. lamarckiana) are still to be found in gardens but are more important as agricultural species.

Many Oenothera species were introduced between 1750 and 1850 and range from rock garden size upwards. Seeds of O. odorata (syn. O. stricta) were purchased in 1790 by Sir Joseph Banks from a ship’s surgeon who had collected them on the coast of Patagonia. The perennial O. tetragona has brilliant yellow flowers which stay open all day and was found by John Frazer during his visit to the southern Appalachians in 1807-1810. In 1811, Bradbury and Nuttall found O. missouriensis during an expedition up the Missouri river. O. acaulis, a dwarf perennial species with white flowers turning to pink, was recommended in late Victorian times as an edging for shrub beds.

Present day encyclopaedias of garden plants will list several species of evening primrose, some with one or even two synonyms, and provide advice on cultivation and propagation. Evening primrose will thrive in any ordinary, well drained garden soil, in an open, sunny site. The National Council for the Conservation of Plants and Gardens, based at Wisley, maintains a national Oenothera collection as part of its National Collections scheme.

The benefits of evening primrose oil

The particular importance in human nutrition of γ-linolenic acid has been elucidated from work initiated in the 1970s by Dr David Horrobin, whilst Professor of Medicine at the University of Montreal. To develop his theories, Dr Horrobin has conducted a thorough programme of research into the role of γ-linolenic acid in the body (Horrobin, 1995).

The main dietary fatty acid is linoleic acid, a polyunsaturated fatty acid well known as a constituent of sunflower oil. To be fully utilised by the body, linoleic acid must be converted into γ-linolenic acid, a reaction catalysed by the enzyme delta-6-desaturase. This conversion can be very slow in individuals suffering from a number or common diseases, and may also be blocked by factors such as ageing, high cholesterol levels, stress, high alcohol intake and diabetes. By administering γ-linolenic acid, in the form of evening primrose oil, substantial clinical improvements can be produced in patients suffering from diseases such as atopic eczema or breast pain.

Although there are other sources of γ-linolenic acid, that in evening primrose oil appears to be the most biologically active. This seems to be because most of the γ-linolenic acid is in the form of Enotherol®, a particular trigyceride consisting of two molecules of linoleic acid and one of γ-linolenic acid on a glycerol backbone. It has been suggested that in Enotherol®, γ-linolenic acid is in its most readily metabolisable form (Horrobin, 1994).

A new agricultural crop

For evening primrose to be an economically viable source of γ-linolenic acid, reliable supplies of good quality seed must be available at acceptable cost and agricultural production was clearly going to be the only way of meeting demand.

Initially, genotypes already available through the seed trade were adopted for oilseed production and the first step in the history of oilseed evening primrose ‘breeding’ was the choice of the most suitable species for agricultural use from those available. It was soon evident that species of the taxonomic subsection Euoenothera, such as O. biennis and O. erythrosepala, were best suited for agricultural use, due to their erect plant habit, high seed yields and high seed oil and GLA contents. However, the wild evening primrose has several characteristics which make it well suited to its natural environment, but which are unacceptable to modern agriculture. Seed dormancy ensures survival in harsh environments, whilst capsule splitting at maturity aids seed dispersal. For farmers, however, the implications are unreliable establishment, lower harvested yields and weed problems in subsequent crops.

Scientists at Writtle College screened over 2000 different races of evening primrose and, despite difficulties imposed by the genetic system of evening primrose, several improved cultivars have been produced. An early success was the identification of ‘closed podded’ types, which retain their seed at maturity. More recently, cultivars with lower seed dormancy, higher yielding ability and improved seed oil contents and quality have been produced. Agricultural evening primrose is now grown in parts of Europe, North America, Asia and Australasia, and the hectarage is steadily increasing.

Future prospects

Although many natural sources of medicines have been replaced by synthetic analogues, it is highly unlikely that factory production of γ-linolenic acid will replace evening primrose. In fact, evening primrose is itself a ‘γ-linolenic acid factory in the field’. The same precise biochemical reactions take place in the developing evening primrose seed to produce an oil remarkably consistent both in γ-linolenic acid content and in the way the γ-linolenic acid is built into the oil. All this is achieved without the need for ‘up front’ capital investment in new buildings or for factories to be built on ‘green field’ sites.

Of course, sales of the product sometimes boom, at other times they dip. It would be difficult to turn a man-made factory on or off in response to demand, and the product is likely to be difficult to store. Not so evening primrose. There seems to be no more effective, convenient way of storing γ-linolenic acid than in evening primrose seed, where it has been shown that the γ-linolenic acid will not deteriorate even after several years of storage.

These days, there is much talk about agricultural diversification and many plants have been suggested as possible new crops. Evening primrose has succeeded since it is both technically feasible to grow on an agricultural scale and because there is a market for the product. Evening primrose oil is now gaining widespread acceptance as a dietary supplement and pharmaceutical. So, too, is the idea of ‘factories in the field’. Other crops are being developed for biomass production or for production of ‘biofuels’ such as diesel substitutes. Evening primrose has been transformed from an attractive, familiar plant of the garden into a biochemical factory more complex and environmentally friendly than any man-made alternative.

Further reading

  • Horrobin, D.F. (1994): Natural ¹ Safe. Pharmaceutical Technology Europe, December 1994. 2pp.
  • Horrobin, D.F. (1995): Lipids for life - Scotia’s commitment to fatty acids. Scrip Magazine, October 1995. 2pp.

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