Dandelion

For other uses, see Dandelion (disambiguation)}}}.

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. The genus is taxonomically very complex, with numerous microspecies, 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.

Dandelion clock

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. 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. The number of blows required to completely rid the clock of its seeds is deemed to be the time of day. 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.

The name dandelion is a derivation of the Old French, dent-de-lion, literally "lion's tooth" on account of the sharply lobed leaves of the plant. In modern French the plant is called pissenlit, "urinate in bed", referring to its diuretic properties. Likewise, "pissabeds" is an English folkname for this plant, "piscialletto" in Italian and "meacamas" In Spanish (otherwise known as "diente de león", lion's tooth).

Seed developement and genetics

As already said, the taxonomical situation of the genus is quite complex, mainly due to the fact that many dandelions are genetically triploid. An odd number of chromosomes usually brings to sterility, but dandelions with such karyotype can reproduce without fertilization, a process called apomixishttp://www.talkorigins.org/faqs/comdesc/section2.html#vestiges. In these individuals flowers are useless vestigial structures, although they may still produce a 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 coutries only triploid and tetraploid apomicts are present. This seems to be linked to higher temperatures, survival of pre-glacial populations and human impact, but the subject is still being studied.

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.
and others.

Eye level view of 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 readily distinguished by their branched flowering stems.

Dandelions are used as food plants by the larvae of some species of Lepidoptera - see list of Lepidoptera which feed on Dandelions.

Cultivation and uses

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 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.

Macro photo of dandelion seed dispersal.

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.

Dandelion flowers can be used to make dandelion wine. The recipe usually contains citrus fruit. Another recipe using the plant is dandelion flower jam. The leaves are high in vitamin A, vitamin C and iron. 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. 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, and authentic recipes are sold by health food shops, but it is not clear whether the cheaper supermarket versions actually contain either plant.

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.

References and external links

Wikimedia Commons has media related to:

[Special]

Richards, A. J. 1972. The Taraxacum flora of the British Isles. Watsonia 9 (supplement): 1-141.
Gail, Peter. The Dandelion Celebration: A Guide to Unexpected Cuisine. Cleveland, Ohio: Goosefoot Acres Press, 1994. ISBN 1879863510.
[How to cook dandelions] ~ at Wikibooks
[Dandelion Poetry, Folklore, Literature, and Pictures]
[Dandelion at Plants For A Future]

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