Taraxacum

These are individual pollen grains of the dandelion - Taraxacum officinale.

Segment of pappus fiber showing barbs

The species of Taraxacum are tap-rooted, perennial, herbaceous plants, native to temperate areas of the Northern Hemisphere. The genus contains many species, which usually (or in the case of triploids, obligately) reproduce by apomixis, resulting in many local populations and endemism. In the British Isles alone, 234 microspecies are recognised in nine loosely defined sections, of which 40 are "probably endemic".[7]

In general, the leaves are 5–25 cm (2" to 10") long or longer, simple, lobed, and form a basal rosette above the central taproot. The flower heads are yellow to orange coloured, and are open in the daytime, but closed at night. The heads are borne singly on a hollow stem (scape) that is usually leafless and rises 1–10 cm (​¹⁄₂" to 4") or more[3] above the leaves. Stems and leaves exude a white, milky latex when broken. A rosette may produce several flowering stems at a time. The flower heads are 2–5 cm (1" to 2") in diameter and consist entirely of ray florets. The flower heads mature into spherical seed heads sometimes called blowballs[8] or clocks (in both British and American English)[9][10][11][12] containing many single-seeded fruits called achenes. Each achene is attached to a pappus of fine hair-like material which enables wind-aided dispersal over long distances.

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 downward to allow the seeds to disperse. The outer bracts are often reflexed downward, but remain appressed in plants of the sections Palustria and Spectabilia. Some species drop the "parachute" from the achenes; the hair-like parachutes are called pappus, and they are modified sepals. Between the pappus and the achene is a stalk called a beak, which elongates as the fruit matures. The beak breaks off from the achene quite easily, separating the seed from the parachute.

Seed dispersal

A number of species of Taraxacum are seed-dispersed ruderals that rapidly colonize disturbed soil, especially the common dandelion (T. officinale), which has been introduced over much of the temperate world. After flowering is finished, the dandelion flower head dries out for a day or two. The dried petals and stamens drop off, the bracts reflex (curve backwards), and the parachute ball opens into a full sphere. When development is complete, the mature seeds are attached to white, fluffy "parachutes" which easily detach from the seedhead and glide by wind, dispersing.

The seeds are able to cover large distances when dispersed due to the unique morphology of the pappus which works to create a unique type of vortex ring[13][14] that stays attached to the seed rather than being sent downstream. In addition to the creation of this vortex ring, the pappus can adjust its morphology depending on the moisture in the air. This allows the plume of seeds to close up and reduce the chance to separate from the stem, waiting for optimal conditions that will maximize dispersal and germination.[15][16]

The pappus of a dandelion seed which aids in the wind-driven dispersal.

Field with flowering dandelions, Tatarstan, Russia

Hawksbeard flower heads and ripe seeds are sometimes confused with dandelions.

A Taraxacum officinale seedhead with only one seed still attached

Many similar plants in the family Asteraceae with yellow flowers are sometimes known as false dandelions. Dandelion flowers are very similar to those of cat's ears (Hypochaeris). Both plants carry similar flowers, which form into windborne seeds. However, dandelion flowers are borne singly on unbranched, hairless and leafless, hollow stems, while cat's ear flowering stems are branched, solid, and carry bracts. Both plants have a basal rosette of leaves and a central taproot. However, the leaves of dandelions are smooth or glabrous, whereas those of catsears are coarsely hairy.

Early-flowering dandelions may be distinguished from coltsfoot (Tussilago farfara) by their basal rosette of leaves, their lack of disc florets, and the absence of scales on the flowering stem.[17]

Other plants with superficially similar flowers include hawkweeds (Hieracium) and hawksbeards (Crepis). These are readily distinguished by branched flowering stems, which are usually hairy and bear leaves.

The genus is taxonomically complex, with some botanists dividing the group into about 34 macrospecies, and about 2000 microspecies;[18] about 235 apomictic and polyploid microspecies have been recorded in Great Britain and Ireland.[19] Some botanists take a much narrower view and only accept a total of about 60 species.[18]

Dandelion in Iran

Selected species

• Taraxacum albidum, a white-flowering Japanese dandelion
• Taraxacum aphrogenes, Paphos dandelion
• Taraxacum brevicorniculatum, frequently misidentified as Taraxacum kok-saghyz, and a poor rubber producer[20]
• Taraxacum californicum, the endangered California dandelion
• Taraxacum centrasiaticum, the Xinjiang dandelion
• Taraxacum ceratophorum, northern dandelion[21]
• Taraxacum erythrospermum, often considered a variety of T. laevigatum[22]
• Taraxacum farinosum, Turkish dandelion
• Taraxacum holmboei, Troödos dandelion
• Taraxacum japonicum, Japanese dandelion, no ring of smallish, downward-turned leaves under the flowerhead
• Taraxacum kok-saghyz, Russian dandelion, which produces rubber[23][20]
• Taraxacum laevigatum, red-seeded dandelion, achenes reddish brown and leaves deeply cut throughout length, inner bracts' tips are hooded
• Taraxacum mirabile
• Taraxacum officinale (syn. T. officinale subsp. vulgare), common dandelion. Found in many forms.
• Taraxacum pankhurstianum
• Taraxacum platycarpum, the Korean dandelion

T. albidum

T. californicum

T. japonicum

T. laevigatum

T. officinale

T. platycarpum

Hand coloured print, plate 1 of Dens Leonis in A Curious Herbal, 1737 by Elizabeth Blackwell

1679 hand coloured print by Maria Sibylla Merian of a dandelion as plant host to the pale tussock moth

Dandelions are thought to have evolved about 30 million years ago in Eurasia.[25] Fossil seeds of Taraxacum tanaiticum have been recorded from the Pliocene of southern Russia.[26] Dandelions have been used by humans for food and as an herb for much of recorded history.[27] They were well known to ancient Egyptians, Greeks and Romans, and are recorded to have been used in traditional Chinese medicine for over a thousand years. The plant was used as food and medicine by Native Americans.[28] Dandelions were brought to North America on the Mayflower for their medicinal benefits.[29]

Leaf resemblance to lion teeth

The Latin name Taraxacum originates in medieval Persian writings on pharmacy. The Persian scientist Al-Razi around 900 CE wrote "the tarashaquq is like chicory". The Persian scientist and philosopher Ibn Sīnā around 1000 CE wrote a book chapter on Taraxacum. Gerard of Cremona, in translating Arabic to Latin around 1170, spelled it tarasacon.[30]

The English name, dandelion, is a corruption of the French dent de lion[31] meaning "lion's tooth", referring to the coarsely toothed leaves. The plant is also known as blowball, cankerwort, doon-head-clock, witch's gowan, milk witch, lion's-tooth, yellow-gowan, Irish daisy, monks-head, priest's-crown, and puff-ball;[32] other common names include faceclock, pee-a-bed, wet-a-bed,[33] swine's snout,[34] white endive, and wild endive.[35]

The English folk name "piss-a-bed" (and indeed the equivalent contemporary French pissenlit) refers to the strong diuretic effect of the plant's roots.[36] In various northeastern Italian dialects, the plant is known as pisacan ("dog pisses"), because they are found at the side of pavements.[37]

In Swedish, it is called maskros (worm rose) after the small insects (thrips) usually present in the flowers.[38] In Finnish and Estonian, the names (voikukka, võilill) translate as butter flower, due to the color of the flower. In Lithuanian, it is known as "Pienė", meaning "milky", because of the white latex that is produced when the stems are cut. The Danish name mælkebøtte (sometimes fandens mælkebøtte) means "milk bin" ("the devils milk bin") and also refers to the milky latex (and its ability to spread). The Welsh (dant-y-llew), German (Löwenzahn), Norwegian (løvetann), Portuguese (dente de leão) and Spanish (diente de león) names mean the same as the French and the English names. In Czech it is known as pampeliška where the "liška" part directly translates to a "fox", possibly due to the colour of the flower.

Plate of sauteed dandelion greens, with Wehani rice

Raw dandelion greens contain high amounts of vitamins A, C, and K, and are moderate sources of calcium, potassium, iron, and manganese.[39] Raw dandelion greens are 86% water, 9% carbohydrates, 3% protein, and 1% fat.[39] A 100 gram (​3 ¹⁄₂oz) reference amount supplies 45 calories.[39]

The raw flowers contain diverse phytochemicals, including polyphenols, such as flavonoids apigenin, isoquercitrin (a quercetin-like compound), and caffeic acid, as well as terpenoids, triterpenes, and sesquiterpenes.[40] The roots contain a substantial amount of the prebiotic fiber inulin. Dandelion greens contain lutein.[41]

Taraxalisin, a serine proteinase, is found in the latex of dandelion roots.[42][43] Maximal activity of the proteinase in the roots is attained in April, at the beginning of plant development after the winter period.[43] Each dandelion seed has a mass(weight) of 500 micrograms or 0.0005g (1/125 of a grain).

• Media related to Taraxacum at Wikimedia Commons