Species of the genus Oenothera L. (Onagra Miller) from the family Onagraceae are characteristic of America, the homeland of species acclimated in Europe. The American flora has the most numerous representatives; plants of these species can be found in natural localities, or they are grown as decorative plants with white, pink to reddish purple, or mostly bright yellow flowers. A few species are also found in Russia. At present, the genus Oenothera is believed to be distributed throughout the world with the exception of Antarctica.
The genus Oenothera is divided into 14 sections. As a result of the creation of hybrid forms, pure single-species populations of this genus are becoming more and more rare. There are two groups of taxonomists, differing in their opinions on its systematics. The total number of Oenothera species is estimated at 123 by American taxonomists, and at 212 by European authors. By 1992, 26 species and permanent hybrids had been found in Poland, grouped in three series: Devriesia (3 species), Oenothera (16 species), and Rugglesia (7 species).
The species of the genus in question are herbaceous plants, annual, biennial or perennial, with single leaves, sometimes bipinnated, without stipels. The radial flowers have four sepals and as many petals, eight stamens in two whorls, and a stigma divided into four lobes. The fruit is a capsule with numerous, tiny, hairless seeds. The flowers of some species are magnificent, usually lemon-colored. Because of the time of day when the flowers bloom, the species Oenothera biennis L. [Onagra biennis (L.) Scop.], for example, is called the night candle. The current knowledge of the genetics of Oenothera has also been published.
Importance of Oenothera Species
Species of the genus Oenothera are widely distributed throughout Europe. They appeared in Europe at the start of the 17th century. The plant was used as a vegetable. Salads were made from the roots, which tasted like ham, and its seeds served as a coffee substitute and as bird food. The leaves and roots were used in folk medicine as remedia metabolica and in homeopathy as antidiarrhoica. Eight species of Oenothera are mentioned in many pharmacopoeias of the world as medicinal plants.
Nowadays, oil obtained from seeds is very important as a natural dietetic and biologically active source of unsaturated fatty acids, especially γ-linolenic acid.
Natural drugs are produced by various firms. Oeparol (Oenothera paradoxa oleum = evening primrose oil) is produced by Agropharm (Poland). One capsule contains 510mg of oil, cold pressed without additions of antioxidants or coloring and aromatic compounds.
The drug must meet specific sensorial and physicochemical requirements. Oeparol has to contain over 73.5% of linoleic acid, and not less than 9% of γ-linolenic acid. Moreover, the drug must be free from pollution, and contain heavy metals only in acceptable amounts. On the basis of the evening primrose oil, the firm Agropharm produces more than 20 different cosmetics and a mosquito-repellent gel.
Horrobin (1990) reported a comparison of biological activity of evening primrose, fungal, blackcurrant, and borage oils, each containing γ-linolenic acid. It was observed that after the application of the same doses of the oils, the highest concentration of final metabolites in the blood of rats (e.g., prostaglandin PGE1) appeared after using evening primrose oil.
The medical importance of evening primrose oil, especially of γ-linolenic acid, was described by Horrobin (1990). Positive results are obtained in the treatment of artheriosclerosis, cardiovascular diseases, atopic eczema, schizophrenia, diabetic neuropathy, multiple sclerosis, Alzheimer’s and Raynaud’s diseases, and others. Besides numerous papers on the therapeutic effects of this oil, some publications report negative results of clinical research.
The aerial part of Oenothera species may also be a source of other biologically active compounds, especially phenolics. Flavonoids with different structures have multidirectional effects on mammals. Other phenol compounds, like phenolic acids and ellagotannins, exhibit pharmacological activity. The hydrolyzable tannins show antitumor activity, and also inhibit HIV replication and Herpes simplex HSV viruses. These compounds are enzyme inhibitors and antioxidants, and they also have antiviral properties.
Oenothera Species (Evening Primrose): Conclusion
Seeds of Oenothera species are a source of bio-oil of consumer and medicinal significance. As a result of our studies with eight Oenothera species, it was found that micropropagation from both shoot tips and nodal segments follows a similar pattern. Eight to 14 shoots can be obtained from a single explant. The cloning of the Oenothera species may find practical application in the case of some particularly interesting varieties.
The oil synthesized in the seeds of O. biennis plants derived from in vitro cultures contains quantities of fatty acids similar to those in the seeds of soil plants. The results are especially interesting for the contents of the C-18:3 acid in the seeds of 1-year-old plants of O. paradoxa and O. ammophila in comparison with its contents in the seeds of 2-year-old plants. Osamu and Tadashi (1987) had earlier reported γ-linolenic acid (6.7%) in the callus tissue of the species mentioned.
Apart from γ-linolenic acid with its diverse pharmacological effects, noteworthy is the occurrence of flavonoids and oenotheins belonging to the ellagotannin group with anticarcinogenic and antiviral properties which have been found in the species O. erythrosepala, O. biennis, and O. laciniata. Preliminary analyses using 2D-TLC indicate the presence of flavonoids, ellagic and gallic acids, and probably their derivatives in callus, multiple shoots, and leaves.
The results of our studies and those of others show that the method of micropropagation from existing meristems can be used in mass production of the Oenothera species while preserving their genetic stability.
Selections from the book: “Medicinal and Aromatic Plants X”, (1998).