Taraxacum
Taraxacum is a genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus has a near-cosmopolitan distribution, absent only from tropical and polar areas. Two of the most common species worldwide, T. officinale and T. erythrospermum, are European species introduced into North America, where they are non-native. Dandelions thrive in temperate regions and can be found in yards, gardens, sides of roads, among crops, and in many other habitats.
Like other members of the family Asteraceae, they have very small flowers collected together into a composite flower head. Each single flower in a head is called a floret. In part due to their abundance, along with being a generalist species, dandelions are one of the most vital early spring [|nectar] sources for a wide host of pollinators. Many Taraxacum species produce seeds asexually by apomixis, where the seeds are produced without pollination, resulting in offspring that are genetically identical to the parent plant.
Etymology
The Latin name Taraxacum derives from the Arabic tarakhshaqūn, meaning "bitter herb". The Arabic term is possibly of Persian origin. Persian polymath Al-Razi used the word tarakhshaqūn in relation to dandelions, chicory, and endives. Al-Razi wrote "the tarakhshaqūn is like chicory, but more efficacious"; it is unclear exactly to which plant Al-Razi referred however. If Persian in origin, the word could have originally meant "bitter purslane" from تلک and چکش. Gerard of Cremona, in translating Arabic to Latin around 1170, spelled it tarasacon.The English name, dandelion, is a borrowing of the French dent de lion 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; other common names include faceclock, pee-a-bed, wet-a-bed, swine's snout, white endive, and wild endive. The English folk name "piss-a-bed" refers to the strong diuretic effect of the plant's leaves. In Swedish, it is called maskros after the thrip nymphs usually present on the plant.
Description
Taraxacum species are tap-rooted, perennial, herbaceous plants, native to temperate areas of the Northern Hemisphere. The genus contains many species, which usually reproduce by apomixis, resulting in many local populations and endemism. In the British Isles alone, 234 microspecies are recognised in nine loosely defined sections. A number of Taraxacum species can act as ruderals, pioneer species that rapidly colonise disturbed soil. The common dandelion has been introduced over much of the temperate world, and it is especially effective at spreading along roads, cemeteries, lawns, and pastures. A week or two after flowering, the dandelion's flower becomes a round seed head. The bracts, specialized leaves around the flower, curve backwards. The parachute ball fully opens into a sphere, and the yellow petals fall away. When development is complete, the mature seeds are attached to white, fluffy "parachutes", which easily detach from the seed head and glide on the wind, dispersing.In general, the leaves are long or longer, simple, lobed-to-pinnatisect, forming a basal rosette above the central taproot. The flower heads range from yellow to orange, and they are open in the daytime, but closed at night. The heads are attached to a hollow stem that is usually leafless and rises or more above the ground. Stems and leaves exude a white, milky latex when broken. A rosette may produce several flowering stems at a time. The flower heads are in diameter and consist entirely of ray florets. The flower heads mature into spherical seed heads, sometimes called blowballs or clocks, containing many single-seeded fruits named cypselae, which are similar to achenes. Each cypsela is attached to a pappus of fine hair-like material, which enables anemochorous dispersal over long distances.
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 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 maximise dispersal and germination.In Taraxacum ovules, the megaspore mother cell is the only cell committed to enter the meiotic process. T. officinale is able to reproduce by a sexual meiotic process involving the production of haploid gametes, as well as by an asexual parthenogenetic meiotic process, referred to as apomixis, that produces diploid seeds genetically identical to the mother plant. Parthenogenesis permits the autonomous development of an unreduced egg cell into an embryo without the requirement of fertilisation.Taraxacum flowers contain various phytochemicals, including polyphenols such as flavonoids apigenin, isoquercitrin, and caffeic acid, as well as terpenoids, triterpenes, and sesquiterpenes. The roots contain a substantial amount of the prebiotic fibre inulin. Dandelion greens contain lutein. Taraxalisin, a serine proteinase, is found in the latex of dandelion roots. Maximal activity of the proteinase in the roots is attained in April, at the beginning of plant development after the winter period. Each dandelion seed produced in the spring weighs about half a milligram. Seeds produced in summer are lighter, around 0.3 mg.
Similar plants
Many plants in the family Asteraceae with yellow flowers are sometimes known as false dandelions. In the case of cat's ear , both plants carry similar flowers, which form into windborne seeds. However, dandelion have unbranched, hairless and leafless, hollow stems, while cat's ear 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, whereas those of cat's ear'' are hairy. Early-flowering dandelions may be distinguished from coltsfoot by their basal rosette of leaves, their lack of disc florets, and the absence of scales on the flowering stem. Other plants with superficially similar flowers include hawkweeds and hawksbeards. These are distinguished by branched stems, which are usually hairy and bear leaves.Classification
The genus is taxonomically complex due to the presence of apomixis; any morphologically distinct clonal population would deserve its own microspecies. About 235 apomictic and polyploid microspecies have been recorded in Great Britain and Ireland alone. Phylogenetic approaches are also complicated by the accelerated mutation in apomixic lines and repeated ancient hybridisation events in the genus.By 1970, the group was divided into about 34 macrospecies or sections, and about 2000 microspecies; By 2015, the number had been revised to include 60 sections and about 2800 microspecies. 30 of these sections are known to reproduce sexually.
Botanists specialising in the genus Taraxacum are sometimes called taraxacologists, such as Gunnar Marklund, Johannes Leendert van Soest and A.J. Richards.
Selected species
- Taraxacum albidum, the white-flowered Japanese dandelion, a hybrid between T. coreanum and T. japonicum
- Taraxacum algarbiense
- Taraxacum aphrogenes, the Paphos dandelion
- Taraxacum arcticum
- Taraxacum balticum
- Taraxacum brachyceras
- Taraxacum brevicorniculatum, frequently misidentified as T. kok-saghyz and a poor rubber producer
- Taraxacum californicum, the California dandelion, an endangered species
- Taraxacum carneocoloratum
- Taraxacum centrasiaticum, the Xinjiang dandelion
- Taraxacum ceratophorum, the horned dandelion, considered by some sources to be a North American subspecies of T. officinale
- Taraxacum coreanum
- Taraxacum desertorum
- Taraxacum erythrospermum, the red-seeded dandelion, often considered a variety of T. laevigatum
- Taraxacum farinosum, the Turkish dandelion
- Taraxacum holmboei, the Troödos dandelion
- Taraxacum hybernum
- Taraxacum japonicum, the Japanese dandelion, no ring of smallish, downward-turned leaves under the flower head
- Taraxacum kok-saghyz, the Kazakh dandelion, which produces rubber
- Taraxacum laevigatum, the rock dandelion, achenes reddish brown and leaves deeply cut throughout the length, inner bracts' tips are hooded
- Taraxacum lissocarpum
- Taraxacum minimum
- Taraxacum mirabile
- Taraxacum officinale, the common dandelion, found in many forms
- Taraxacum pankhurstianum, the St. Kilda dandelion
- Taraxacum platycarpum, the Korean dandelion
- Taraxacum pseudoroseum
- Taraxacum rubifolium
- ''Taraxacum suecicum''
Cultivars
- 'Amélioré à Coeur Plein' yields an abundant crop with minimal ground space because its leaves clump rather than spreading out.
- 'Broad-leaved' - The leaves are thick and tender. It grows up to 60 mm wide depending on the soil.
- 'Vert de Montmagny' is a large-leaved, vigorous grower, which matures early.
History