Taraxacum officinale (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, plant habit; 2, inner involucral bract; 3, flower; 4, fruit; 5, upper part of achene (Achmad Satiri Nurhaman)

Taraxacum officinale Weber

Protologue: Prim. fl. holsat.: 56 (1780).

Family: Compositae

Chromosome number: 2n= 16, 24, 32, 40, 48

Vernacular names

• Dandelion (En)
• Pissenlit, dent de lion (Fr)
• Indonesia: jombang (Java)
• Vietnam: bồ công anh, sư nha.

Distribution

Dandelion is native to Europe and continental temperate Asia south to the Himalayas, but now distributed almost all over the world. In the Malesian region it has been introduced and naturalized in Peninsular Malaysia, West Java and the Philippines (Benguet Province). It is sometimes cultivated as a vegetable or for medicinal applications.

Uses

Infusions or decoctions of dried roots, leaves or simply the entire plant of dandelion are widely used as a general tonic, anti-inflammatory, depurative, cholagogue, diuretic, mild laxative, and for kidney and liver disorders. Infusions are also recommended in the treatment of skin problems, such as acne, eczema, psoriasis and even for arthritic and rheumatic complaints. Externally the latex is applied to boils and other skin infections or applied as a poultice on inflamed wounds. In South-East Asia, dandelion is a fairly recently introduced weed, so traditional uses are very limited. In Indo-China it is used as a diuretic and cholagogue. In India, the roots are applied as a tonic, diuretic, mild laxative, and chiefly used in kidney and liver disorders. In China, the leaves are prescribed internally as a bitter depurant, in the treatment of breast and lung tumours, mastitis, abscesses, jaundice, and urinary tract infections; and externally to treat snake bites. In Europe and North America, the leaves and roots, fresh or dried, are used as a mild laxative, a diuretic and for the treatment of high blood pressure by reducing the volume of fluid in the body. The roots accelerate steady elimination of toxins, by working principally on liver and gall bladder to help remove waste products, and simultaneously stimulating the kidneys to remove toxins in the urine. The leaves or roots may also help to prevent or even dissolve gallstones. A decoction of the roots is used as an antidiabetic.

The leaves are also eaten as a vegetable. When grown without light (artificially or when covered with earth) the pale leaves are more brittle and taste better. The young and unopened flower heads can be used as capers. In North Africa the leaves are used as a seasoning. The bitter leaves are also applied in wines, beers and non-alcoholic drinks. The ground roots are used as a substitute for coffee. In spring the flowers contain much nectar and are locally important for the production of honey. Formerly, dandelions were cultivated in Japan for ornamental purposes.

Production and international trade

In Germany, France and the United States dandelion is comparatively often cultivated as a vegetable. It is also cultivated in India, where it is a popular remedy for liver complaints. However, no statistics are available on production and trade.

Properties

Phytochemical analysis has revealed chicoric acid and monocaffeyltartaric acid to be the major phenolic constituents of flowers, roots, leaves and involucral bracts of T. officinale. These compounds are also the main phenolic constituents of some common dandelion preparations, e.g. dandelion tea, root coffee and root capsules. Furthermore, the presence of sesquiterpene lactones (germacranolide type, as glucosides), triterpenes (e.g. cycloartenol) and flavonoids (apigenin-7-glucoside, luteolin-7-glucoside) in the leaves is reported in literature.

As with many Compositae, the roots of dandelion also have a high content of inulin, a polysaccharide based on fructose. This compound serves as a food reserve and can reach levels as high as 25% in autumn in the temperate zones. Inulin can be used as a sugar substitute, which is of interest for diabetic patients. Furthermore, the hypoglycaemic activity of this compound is sometimes mentioned in literature, though many reports are not conclusive in this respect. On the other hand, hypoglycaemic activity of dandelion preparations have been observed in various animal models: the 50% ethanol-water extract of the entire plant at a dose of 250 mg/kg orally in rats, dried entire plants at doses of 1-2 g/kg administered intragastrically to rabbits and a water extract of dried roots at a dose of 25 mg/kg administered intragastrically to mice all showed hypoglycaemic activities.

The high potassium content of dandelion, especially in the leaves (up to 4.5% of the dry weight) is considered to be responsible for the well-known diuretic activity, which has been confirmed in various animal models. The ethanol (30%) extract of dandelion roots, administered orally at a dose of 0.1 ml/kg in male rats, shows diuretic activity. In experiments with mice and rats the diuretic and saluretic indices of a fluid extract of dandelion, corresponding to approximately 8 g dried aerial parts/kg body weight, were comparable to those of furosemide (80 mg/kg body weight) a well-known diuretic. The high potassium content ensures that potassium eliminated in the urine is replaced. Furthermore, in dogs, the volume of bile doubled when a decoction of fresh leaves (equivalent to 5 g of dried plant material) was administered intravenously. In rats, a choleretic effect was observed following administration of a 5% dandelion extract (2 ml) by means of a cannula, and in another experiment, an alcoholic extract of the whole plant administered to rats gave a 40% increase in bile secretion.

The anti-inflammatory activity of dandelion has been investigated in several animal models. A methanol extract of dandelion leaves, at a dose of 2.0 mg/ear applied externally, reduced swelling and inflammation in mice with 12-0-tetradecanoylphorbol-13-acetate (TPA)-induced ear inflammations. Furthermore, a 95% ethanol extract of dried dandelion leaves, administered intraperitoneally in rats with carrageenan-induced pedal oedema at a dose of 0.1 g/kg showed anti-inflammatory activity. Finally, the 80% ethanol extract of dried dandelion roots administered by gastric intubation at a dose of 100 mg/kg in male rats showed 25% inhibition of oedema in a carrageenan-induced pedal oedema model, in comparison with 45% inhibition of indomethacin (5 mg/kg) in the same experiment.

Other pharmacological activities include: a dose-dependent inhibition of the ADP-induced aggregation of human platelets by an ethanolic extract of the roots of T. officinale. A bioguided purification revealed activity in two fractions: one containing low-molecular weight polysaccharides, and one fraction characterized by the presence of triterpenes/steroids. A 95% ethanol extract of dried dandelion leaves administered to mice intragastrically at a dose of 1.0 g/kg, and intraperitoneally at a dose of 0.1 g/kg, exhibited analgesic activity in both the phenylquinone-induced writhing and the hot plate models. The water extract of dandelion roots administered intragastrically at a dose of 2 g/kg in rats with ETOH-HCl-induced ulcerations showed a strong anti-ulcer activity. However, the methanol extract at the same dose shows only weak activity. The hot water extract of dried dandelion aerial parts given intraperitoneally at doses of 30-40 mg/kg exhibited antitumour activities against CA-C3H/HE-MM46 and fibrosarcoma METH-1 in mice.

The 70% ethanol extract of dried dandelion aerial parts at concentrations of 2, 10 and 50% showed acaricide activity against Tetranychus urticae, with percentages of inhibition being respectively 57, 90 and 100%. Both ether and methanol extracts of fresh aerial parts used at undiluted concentrations in the disk method showed antifungal activity against Aspergillus flavus. Furthermore, the tincture (10%) of dried leaves at a concentration of 0.1 ml/disk showed antibacterial activity against Bacillus subtilis.

Lettucenin A is a sesquiterpenoid phytoalexin produced by a number of Compositae including T. officinale to protect themselves against microorganisms. In a liquid cell culture 16.4 µg/g fresh weight inhibits the growth of the fungus Cladosporium herbarum; the lettucenin A production peaked only 2-6 hours after infection.

An analysis of leaves and flowers from Pakistan gave per 100 g edible portion: water 88.8 g, protein 3.6 g, ether extracts 1.6 g, total carbohydrates 3.7 g, fibre 0.4 g, and ash 2.3 g, phosphorus 59 mg, calcium 474 mg, iron 3.3 mg and vitamin C 73 mg. In vitro dry-matter digestibility is about 80%. The latex from dandelion may cause skin irritation. The sugar content of the nectar is around 50%. The sugars are mainly glucose and fructose, and a smaller proportion of sucrose. The pollen contains about 15% of protein.

Adulterations and substitutes

Roots of Cichorium intybus L. are used as a substitute for the roots of dandelion. They are also rich in inulin, and bitter due to sesquiterpenoid lactones.

Description

• A perennial, stemless, polymorphous herb up to 30(-50) cm tall, with a long taproot and latex in all parts.
• Leaves arranged spirally in a radical rosette, oblanceolate to narrowly spathulate, 4-35 cm × 0.7-10 cm, very variably and irregularly pinnatilobed to pinnatipartite, variably hairy or rarely completely glabrous, almost distinctly petiolate or narrowly tapering into a winged petiole, petiole green or pink to purplish.
• Inflorescence an axillary head, 1-25 per plant, peduncle simple, hollow, leafless, (3-)3.5-5(-6.5) cm in diameter, outer involucral bracts many-seriate, patent to recurved, ovate to linear-lanceolate, unequal, without "horns" (thickened and/or clawed apices), inner involucral bracts 1-seriate, erect, oblong, receptacle flat, naked.
• Flowers many, all ligulate; corolla yellow, but often with a purple line outside; stamens 5, anthers fused into a tube, sagittate at base; ovary inferior, with a single ovule; style 1, greenish or yellowish to black, stigmas 2, spreading.
• Fruit an achene, narrowly obovoid, about 3 mm long, ribbed, greenish to straw-coloured or brownish, the upper third minutely spiny, abruptly contracted into a 6-12 mm long beak which is crowned by spreading, scabrid, white pappus hairs.
• Seedling with epigeal germination; cotyledons free, leafy, obspathulate, sheathed at base; epicotyl absent; all leaves alternate.

Growth and development

Both sexually and asexually reproducing populations of T. officinale exist. The sexually reproducing plants are generally obligate cross-pollinators, although exceptions have been reported. The self-compatibility is hereditary. The asexual reproduction is known as agamospermy, and functions only in polyploid plants. It may be obligatory or facultative, even within a single head.

The flowers produce nectar and pollen that attract insects, mainly bees, which pollinate the flowers. Most of the orange-coloured pollen is released between 10-12 h in the morning, and some 20-75% is sterile. Wind can disperse the seeds over long distances by means of their "parachute"-like pappus.

Other botanical information

Taraxacum is closely related to the genus Crepis, and belongs to the tribe Lactuceae. It has been subdivided into some 40 sections. T. officinale sensu lato forms a large and highly variable polyploid complex. The agamospermous reproduction results in a high number of uniform "clones", which have often been described as microspecies or agamospecies. T. officinale sensu stricto belongs to section Ruderalia J. Kirschn., H. Ollg. & Stepanek (synonym: section Vulgaria Dahlst. p.p.) with about 1000 microspecies. Some authors prefer to distinguish many taxa at subspecific rank while recognizing only a few species within Taraxacum. The section Ruderalia is likely to be of recent origin, as it harbours the more advanced microspecies. These are often polyploid and tend to possess more satellite chromosomes than generally diploid primitive microspecies. The length of the beak on the achene generally increases with increasing ploidy level.

The microspecies T. javanicum v. Soest has been described from Java, and belongs to T. officinale sensu lato. Recently, another microspecies, T. indonesicum Sonck has been described from West Java. Although the two are clearly distinct to specialists, it is likely that both are used in a similar way by local people.

Cultivars are available, e.g. "Amélioré Géant".

Ecology

Being weedy in nature, T. officinale is most often found in ruderal places, along roads and fields and in grassland. In tropical regions it occurs only at higher elevations, in Malesia at 1200-1500 m altitude. It occurs on various soils, from sandy dunes to thick clay, and from dry to wet, sometimes even brackish habitats, though it seems to grow best on fertile sandy or loamy soils.

Propagation and planting

Propagation of dandelion is by seed or by division. In Europe about 60% of all achenes germinate in the year of production; about 30% in the next year and about 5% in the year thereafter. A neglectable percentage germinates after 5 years. The viability of fresh achenes is 70-100%, but drops rapidly when stored dry at 20 °C; cool and dry storage does not cause a rapid decrease in viability. Achenes germinate best at temperatures of 20-25 °C, with a daily fluctuation of about 5 °C. They should not be sown deeper than 1 cm as this will affect fast and uniform emergence.

In vitro production of active compounds

Undifferentiated cultured cells of dandelion produce oleanolic and ursolic acids as major triterpenoids, in addition to triterpenols composed mainly of α- and β-amyrins. Regenerated and wild plants contain additional triterpenols (taraxasterol and lupeol), but negligible quantities of triterpene acids. Squalene synthase activity has been detected in the microsomal fractions of suspension-cultured cells of T. officinale, which produce cycloartane (involved in phytosterol biosynthesis) and other triterpenoids e.g. oleanane and ursane.

Husbandry

Injured roots or small parts of roots of dandelion can regenerate and develop new rosettes. Therefore mechanical control of T. officinale as a weed is not effective. In Canada, ethalfluralin proved an effective herbicide for dandelion cultivation with no residues in the roots.

Diseases and pests

Diseases observed in dandelion in the temperate zones include Agrobacterium tumefaciens, and fungi like Synchytrium taraxaci, Bremia lactucae, Protomyces pachydermus, Sphaerotheca fuliginea, Puccinia spp., Ramularia taraxaci and Septoria taraxaci. Pests include the nematodes Ditylenchus dipsaci and Meloidogyne hapla and the beetle Ceutorhynchus punctiger, whereas various other insects, spiders, snails, birds and mammals feed on dandelion in some way or another.

Harvesting

Dandelion roots are harvested at the end of the growing season, when inulin contents are highest.

Yield

In India, cultivated dandelion yields about 1650 kg of roots per ha. In Canada, the dry matter production of roots was about 2300 kg/ha, i.e. 19% higher when planted at a high density of over 114 000 plants/ha compared to a lower density of about 89 000 plants/ha. Average root production per dandelion plant with the flower buds removed was 40 g when grown in a nutrient solution and 30 g when grown on a peat substrate with organic fertilizer.

Handling after harvest

In India, roots of dandelion are washed, dried and subsequently stored in containers to which a few drops of carbon tetrachloride have been added as preservative.

Genetic resources and breeding

T. officinale is such a widespread weed that its genetic basis does not seem to be at risk; this is not the case for some of its microspecies. Breeding efforts have been directed to a more palatable crispy vegetable rather than to its medicinal properties.

Prospects

As a result of the quite well investigated diuretic properties, dandelion preparations could be used as an adjunct to treatments where enhanced urinary output is desirable, for example, the prevention of renal gravel or frequently returning uncomplicated urinary tract infections. Other pharmacological actions (e.g. on the billary excretion) are also interesting, but merit further research.

Literature

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Authors

• Wongsatit Chuakul