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Dandelion

2007 Schools Wikipedia Selection. Related subjects: Plants

                 iDandelion
         Scientific classification

   Kingdom:  Plantae
   Division: Magnoliophyta
   Class:    Magnoliopsida
   Order:    Asterales
   Family:   Asteraceae
   Genus:    Taraxacum
             Cass.

                                   Species

   See text

   A dandelion is a short plant, usually with a yellow flower head and
   notched leaves. A dandelion flower head consists of many tiny flowers.
   The dandelion is native to Europe and Asia, and has spread to many
   other places. The dandelion is also known by its generic name
   Taraxacum. In Northern areas and places where the dandelion is not
   native, it reproduces asexually.

Description

   Dandelion (Taraxacum) is a large genus of flowering plants in the
   family Asteraceae. They are tap-rooted biennial or perennial herbaceous
   plants, native to temperate areas of the Northern Hemisphere of the Old
   World.
   A flowering dandelion.
   Enlarge
   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.

   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

   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 "dandelion clock", and blowing it
   apart is a popular pastime for children. In German it's called a
   Pusteblume, translated as "blow flower". The number of blows required
   to completely rid the clock of its seeds is deemed to be the time of
   day.

Seeds

   Macro photo of dandelion seed dispersal.
   Enlarge
   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 beak, which elongates as the fruit
   matures. The beak breaks off from the achene quite easily.

Name

   The name dandelion is derived from the Old 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. The first written
   usage of the word occurs in an "herbal" dated 1373, but there is a 1363
   document in which the word "dandelion" was used as a proper name
   (Willelmus Dawndelyon).

   In German, the dandelion is called Löwenzahn, which is also translated
   as "lion's tooth." 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, 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".

Selected species

     * Taraxacum officinale (syn. T. 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

   As aforementioned, 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, a
   process called apomixis. 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 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

   The dandelion's taproot, shown 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.
   Enlarge
   The dandelion's taproot, shown 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, 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.

   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.
   Eye level view of dandelions
   Enlarge
   Eye level view of dandelions

   Dandelion root is a registered drug in Canada, sold as a diuretic. A
   leaf decoction can be drunk to "purify the blood", for the treatment of
   anaemia, 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 are sold by health food
   shops, but it is not clear whether the 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.

   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).

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. However, more recent research shows that bacteria present in the
   rats' guts may alter the formation of metabolites of Caffeic acid. and
   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.

   Retrieved from " http://en.wikipedia.org/wiki/Dandelion"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
