Dandelion
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The common name Dandelion is given to species of the genus Taraxacum, a large genus of flowering plants in the family Asteraceae. In the Asteraceae (formerly Compositae) the 'flowers' are morphologically a composite flower head consisting of many tiny flowers called florets. The dandelion is native to Europe and Asia, and has been introduced to many other places. In northern areas and places where the dandelion is not native, it has become a weedy species, exploiting disturbed ground in human environments. Taraxacum species reproduce asexually by means of apomixis and seed production commonly occurs without pollination.http://128.104.239.6/uw_weeds/extension/articles/dandelion.htm
Description
Dandelions are tap-rooted biennial or perennial herbaceous plants, native to temperate areas of the Northern Hemisphere of the Old World. They are commonly known as weeds or ruderals. The genus is taxonomically very complex, with numerous macrospecies, and polyploidy is also common; over 250 species have been recorded in the British Isles alone (Richards 1972). Some botanists take a much narrower viewpoint, and only accept a total of about 60 species.The leaves are 5-25 cm long, simple and basal, entire or lobed, forming a rosette above the central taproot. As the leaves grow outward they push down the surrounding vegetation, such as grass in a lawn, which kills other plants by cutting off their access to sunlight. A bright yellow flower head (which is open in the daytime but closes at night) is borne singly on a hollow stem (scape) which rises 4-30 cm above the leaves and exudes a milky sap (latex) when broken. A rosette may produce several flowering stems at a time. The flower head is 2-5 cm in diameter and consists entirely of ray florets. Dandelions are used as food plants by the larvae of some species of Lepidoptera. See List of Lepidoptera that feed on dandelions.Away from their native regions, they have become established in the Americas, Australia and New Zealand as weeds. They are now common plants throughout all temperate regions.The flower matures into a globe of fine filaments that are usually distributed by wind, carrying away the seed-containing achenes. This globe (receptacle) is called the "clock".False dandelions
Dandelions are so similar to catsears (Hypochoeris) that catsears are also known as "false dandelions." Both plants carry similar flowers which form into windborne seeds. However, catsear flowering stems are forked and solid, whereas dandelions possess unforked stems that are hollow. Both plants have a rosette of leaves and a central taproot. However, the leaves of dandelions are jagged in appearance, whereas those of catsear are more lobe-shaped and hairy. Other plants with similar flowers include hawkweeds (Hieracium) and hawksbeards (Crepis). These are both readily distinguished by their branched flowering stems.Seeds
The flower head is surrounded by bracts (sometimes mistakenly called sepals) in two series. The inner bracts are erect until the seeds mature, then flex down to allow the seeds to disperse; the outer bracts are always reflexed downward. Some species drop the "parachute" (called a pappus, modified sepals) from the achenes. Between the pappus and the achene, there is a stalk called a beak, which elongates as the fruit matures. The beak breaks off from the achene quite easily. After pollination, the dandelion flower dries out for about 10 days and then the seed-bearing parachutes expand and lift out of the dried flower head. The dried part of the flower drops off and the parachute ball opens into a full sphere. The parachute drops off when the seed strikes an obstacle. Often dandelions can be observed growing in a crevice near a wall, because the blowing fruits hit the wall and the feathery pappi drop off, sending the dandelion seeds to the base of the obstacle where they germinate. After the seed is released, the parachutes lose their feathered structure and take on a fuzzy, cotton-like appearance, often called "dandelion snow."Selected species
Origin of the Name
The English name dandelion is a corruption of the French dent de lionS. Potter & L. Sargent (1973) Pedigree: essays on the etymology of words from nature. Collins New Naturalist series Volume 56 meaning lion's tooth, referring to the coarsely-toothed leaves. The names of the plant have the same meaning in several other European languages, such as Italian dente di leone, Spanish diente de león, Portuguese dente-de-leão, Norwegian Løvetann, and German Löwenzahn.
In modern French the plant is called pissenlit, which means "urinate in bed", apparently referring to its diuretic properties. Likewise, "pissabeds" is an English folkname for this plant, piscialletto in Italian and in Spanish it is known as the meacamas.
In Turkish the dandelion is called karahindiba meaning "black endive".
Hungarian names are kutyatej ("dog milk", referring to the white sap found in the stem) and gyermekláncfű ("child's chain grass", referring to the habit of children to pick dandelions, remove the flowers, and make links out of the stems by "plugging" the narrow top end of the stem into the wider bottom end).
Lithuanian name kiaulpienė can be translated as "sow Sonchus" (because plant Sonchus that has white sap also in Lithuanian is pienė (from pienas "milk)) or "sow milk". In Finnish it is called 'voikukka'("butter flower") referring to its buttery colour.
Seed development and genetics
As previously mentioned, the taxonomical situation of the genus is quite complex, mainly because many dandelions are genetically triploid. An odd number of chromosomes usually is associated with sterility, but dandelions with this karyotype can reproduce without fertilization, by a process called apomixis.http://fieldcrop.msu.edu/documents/GR03-050.pdf In these individuals flowers are useless vestigial structures, although they may still produce a small percentage of fertile pollen, keeping some genetic contact with sexual individuals. Diploid dandelions develop seeds after cross-pollination and are outcrossing, or self-incompatible. In most zones of southern Europe and Asia, dandelion populations are sexual or mixed sexual-apomictic, while in northern countries only triploid and tetraploid apomicts are present, as is in the zones where it is not native. This seems to be linked to higher temperatures, survival of pre-glacial populations and human impact, but the subject is still being studied.There are usually 54 to 172 seeds produced per head, but a single plant can produce more than 2000 seeds a year. It has been estimated that more than 97 000 000 seeds/hectare could be produced every year by a dense stand of dandelions.Uses
While the dandelion is considered a weed by many gardeners and lawn owners, the plant does have several culinary uses, and the specific name officinalis refers to its value as a medicinal herb. Dandelions are grown commercially at a small scale as a leaf vegetable. The plant can be eaten cooked or raw in various forms, such as in soup or salad. They are probably closest in character to mustard greens. Usually the young leaves and unopened buds are eaten raw in salads, while older leaves are cooked. Raw leaves have a slightly bitter taste. Dandelion salad is often accompanied with hard boiled eggs. The leaves are high in vitamin A, vitamin C and iron, carrying more iron and calcium than spinach.An article about dandelion nutrition.Dandelion flowers can be used to make dandelion wine, for which there are innumerable recipes http://winemaking.jackkeller.net/dandelion.asp. It has also been used in a saison ale called Pissenlit (literally "wet the bed" in French) made by Brasserie Fantôme in Belgium. Another recipe using the plant is dandelion flower jam. Ground roasted dandelion root can be used as a coffee substitute.
Dandelion root is a registered drug in Canada, sold principally as a diuretic. A leaf decoction can be drunk to "purify the blood", for the treatment of anemia, jaundice, and also for nervousness. Drunk before meals, dandelion root coffee is claimed to stimulate digestive functions and function as a liver tonic. "Dandelion and Burdock" is a soft drink that has long been popular in the United Kingdom with authentic recipes sold by health food shops. It is unclear whether cheaper supermarket versions actually contain extracts of either plant.The milky latex has been used as a mosquito repellent; the milk is also applied to warts, helping get rid of them without damaging the surrounding skin. Yellow or green dye colours can be obtained from the flowers but little colour can be obtained from the roots of the plantA. Dyer (1976) Dyes from natural sources. G. Bell & Sons Ltd., London.
This plant also is useful in farming, because its deep, strong roots break up hardpan.Antioxidant properties
Dandelion contains luteolin, an antioxidant, and has demonstrated antioxidant properties without cytotoxicity.Chun Hu and David D. Kitts. Food, Nutrition and Health, Faculty of Agricultural Sciences, University of British Columbia, Vancouver, BC, Canada. October 2004. Luteolin and luteolin-7-O-glucoside from dandelion flower suppress iNOS and COX-2 in RAW264.7 cells. Springer Netherlands. 245:1-2(107-113). [http://www.springerlink.com/content/qg16p71737602150/]Caffeic acid and carcinogenicity
Caffeic acid is a secondary plant metabolite produced in dandelion, yarrow, horsetail and whitethorn. Despite its name, it is totally unrelated to caffeine. Recent studies have revealed this acid may be carcinogenic. Caffeic acid was tested for carcinogenicity by oral administration in mice, it produced renal cell adenomas in females, and a high incidence of renal tubular cell hyperplasia in animals of each sex.Caffeic acid phenethyl ester is a potent and specific inhibitor of activation of nuclear transcription factor NF-kappa B., Natarajan K, Singh S, Burke TR Jr, Grunberger D, Aggarwal BB., Proc. Natl. Acad. Sci. U S A., 1996 Aug 20;93(17):9090-5. However, more recent research shows that bacteria present in the rats' guts may alter the formation of metabolites of caffeic acid. [http://www.pnas.org/cgi/content/abstract/69/6/1413] and [http://jn.nutrition.org/cgi/content/full/133/6/1853] Also, there have been no known ill-effects of caffeic acid in humans.Next Page
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