Dandelion

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Dandelion
File:Macro dandelion Fcb981.JPG
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Asterales
Family: Asteraceae
Genus: Taraxacum
Cass.
Species

See text

The 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 spread 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.[1]

Description

Dandelion 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.

File:Tom's pictures2 005.jpg
A flowering dandelion.

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, killing the vegetation by cutting off the 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 which 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.

Dandelion clock

File:Taraxacum seed 1.jpg
A dandelion clock.

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".


Seeds

File:Photos-photos 1088103921 Floating.jpg
Macro photo of dandelion seed dispersal.

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.

Name

The name dandelion is derived from the French, dent-de-lion, which is literally "lion's tooth", referring to the sharply-lobed leaves of the plant. The English spelling reflects the French pronunciation at the time this French word was absorbed into English.[2] The first written usage of the word occurs in a herbal dated 1373, but there is a 1363 document in which the word "dandelion" was used as a proper name (Willelmus Dawndelyon).

In Norwegian, the dandelion is called Løvetann, which is also translated as "lion's tooth", also Löwenzahn ("lions' tooth") in German. In bed", apparently referring to its diuretic properties. Likewise, "pissabeds" is an English folkname for this plant, and "piscialletto" is one of its folknames in Italian (with "dente di leone", meaning "lion's tooth"). Similarly in Spanish, it is known as the "meacamas", but also commonly "diente de león". In Portuguese, its common name is "dente-de-leão" meaning also "lion's tooth". 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

Selected species

  • Taraxacum officinale (syn. T. officinale subsp. vulgare), Common Dandelion. Found in many forms, but differs at least from the following species:
  • Taraxacum albidum, a white-flowering Japanese dandelion.
  • Taraxacum japonicum, Japanese dandelion. No ring of smallish, downward-turned leaves under the flowerhead.
  • Taraxacum laevigatum (syn. T. erythrospermum), Red-seeded Dandelion; achenes reddish brown and leaves deeply cut throughout length. Inner bracts' tips are hooded.

Seed development and genetics

File:Dandelion Microscopic 1.jpg
A microscopic view of a dandelion clock showing the pericarp and the achenes.

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.[3] 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.

Dandelion Snow

File:Dandelion Microscopic 2.jpg
A microscopic view of a pappus from a dandelion clock.

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."

Uses

File:Dandelion Blackwell 0136.jpg
The dandelion's taproot, on left in this drawing, makes this plant very difficult to uproot; the top of the plant breaks away, but the root stays in the ground and can sprout again.

While the dandelion is considered a weed by many gardeners and lawn owners, the plant does have several culinary and medicinal uses. 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.[4]

Dandelion flowers can be used to make dandelion wine. The recipe usually contains citrus fruit. Another recipe using the plant is dandelion flower jam. Ground roasted dandelion root can be used as a coffee substitute. Drunk before meals, it is believed to stimulate digestive functions. Sold in most health food stores, often in a mixture, it is considered an excellent cleansing tonic for the liver.

Dandelion root is a registered drug in Canada, sold as a diuretic. Dandelions are so potent in this effect, that children have been known to wet the bed the night after skin contact from playing with them.[2] A leaf decoction can be drunk to "purify the blood", for the treatment of anemia, jaundice, and also for nervousness. 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. A dye can also be obtained from the roots of the plant. A new mixture of roasted roots is sold as a product called DandyBlend which tastes like coffee after the inulin in the dandelion is roasted.

"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 either plant.

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.[5][1]

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.[6] However, more recent research shows that bacteria present in the rats' guts may alter the formation of metabolites of caffeic acid. [2] and [3] Also, there have been no known ill-effects of caffeic acid in humans.

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.

See also

References and external links

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  1. http://128.104.239.6/uw_weeds/extension/articles/dandelion.htm
  2. 2.0 2.1 "Living Green, Dandelions: Time to throw in the trowel - Pesticide bylaws make it easier". CBC.ca In Depth. Jun 13, 2007. Retrieved 2007-06-14. 
  3. http://fieldcrop.msu.edu/documents/GR03-050.pdf
  4. An article about dandelion nutrition.
  5. 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).
  6. 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.
bg:Глухарче

cs:Pampeliška_lékařská da:Mælkebøtte de:Löwenzahn (Taraxacum) et:Võililleo:Leontodo fa:قاصدکko:민들레속 hsb:Mlóč (ród) hr:Maslačak id:Randa Tapak os:Къаппа-къуппа is:Túnfífill it:Tarassaco lt:Kiaulpienė hu:Gyermekláncfű nl:Paardenbloemno:Løvetanner nn:Løvetannsco:Dandillie simple:Dandelion sl:Regrat sr:Маслачак fi:voikukka sv:Maskrosor


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