Taraxacum officinale, the dandelion or common dandelion, is a herbaceous perennial flowering plant in the daisy family, Asteraceae. The common dandelion is well-known for its yellow flower heads that turn into round balls of many silver-tufted fruit, which disperse in the wind. These balls are sometimes called "clocks" or "blowballs". Originally native to Eurasia, as a result of its hardiness and easy propagation, the dandelion has become widely established across several continents. It has been introduced to southern Africa, the Americas, Australia, and New Zealand. It grows in temperate regions of the world in areas with moist soils. They are able to grow in a variety of environments and are tolerant of crowding, extreme temperatures, and low moisture. The dandelion is often considered a weed, especially in lawns, but it is increasingly being recognised in its native regions as useful for attracting birds and pollinating insects. In one study, it ranked as the fourth most important source of pollen. Although dandelion pollen is considered to be an early food resource for some emerging pollinators in spring, it has also been found to lack certain essential nutrients and can lead to declining brood health for bees. The leaves, flowers, and roots are sometimes used as food and in herbal medicine.
Description
Taraxacum officinale grows from a (generally unbranched) taproot and produces several hollow, leafless flower stems, typically 5–40 centimetres (2–15+3⁄4 inches) tall, but occasionally reaching up to 70 cm (28 in) tall. The stems can be tinted purplish, are upright or lax, and produce flower heads that are held as tall or taller than the foliage. The foliage may be upright-growing or horizontally spreading; the leaves have petioles that are either unwinged or narrowly winged. The stems can be glabrous or sparsely covered with short hairs. Plants have milky latex, and the leaves are all basal; each flowering stem lacks bracts and has one single flower head. The yellow flower heads lack receptacle bracts, and all the flowers, which are called florets, are ligulate and bisexual. In many lineages, the seeds are mostly produced by apomixis, even though the flowers are frequently visited by diverse insects. The leaves are 5–45 cm (2–17+3⁄4 in) long and 1–10 cm (1⁄2–4 in) wide, and they are oblanceolate, oblong, or obovate in shape, with the bases gradually narrowing to the petiole. The leaf margins are typically shallowly lobed to deeply lobed and often lacerate or toothed with sharp or dull teeth. The calyculi (the cuplike bracts that hold the florets) are composed of 12 to 18 segments; each segment is reflexed and sometimes glaucous. The lanceolate-shaped bractlets are arranged in two series, with acuminate apices. The 14–25 millimetres (1⁄2–1 in) wide involucres are green to dark green or brownish-green, with dark grey or purplish tips. The florets number 40 to over 100 per head, having yellow or orange-yellow corollas. The fruit, called cypselae, range in colour from olive-green or olive-brown to straw-coloured or greyish; they are oblanceoloid in shape and 2–3 mm (1⁄16–1⁄8 in) long, with slender beaks. The fruit have 4 to 12 ribs that have sharp edges. The silky pappi, which form the parachutes, are white to silver-white in colour and around 6 mm wide. Plants typically have 24 or 40 pairs of chromosomes, while some have 16 or 32 pairs.
Chemistry
Taraxalisin is a serine proteinase found in the latex of dandelion roots. Rudenskaya et al. (1998) found that taraxalisin hydrolyzes a chromogenic peptide substrate Glp-Ala-Ala-Leu-pNA optimally at pH 8.0. Maximal activity of the proteinase in the roots is attained in April, at the beginning of plant development after the winter period.
Taxonomy Carl Linnaeus named the species Leontodon taraxacum in 1753. The current genus name Taraxacum derives possibly from the Arabic Tharakhchakon, or from the Greek Tarraxos. The specific name officinalis refers to its value as a medicinal herb, and is derived from the word opificina, later officina, meaning a workshop or pharmacy. The taxonomy of the genus Taraxacum is complicated by apomictic and polyploid lineages, and the taxonomy and nomenclatural situation of T. officinale is not yet fully resolved. The taxonomy of this genus has been complicated by the recognition of numerous species, subspecies and microspecies. For example, the UK flora currently includes 239 species (of which 58 endemic and 45 non-native), and Rothmaler's Flora of Germany accepts roughly 70 microspecies. T. officinale has a fossil record that goes back to glacial and interglacial times in Europe.
European dandelions Taraxacum officinale L. (dandelion) is a vigorous weed in Europe with diploid sexual populations in the southern regions and partially overlapping populations of diploid sexuals and triploid or tetraploid apomicts in the central and northern regions.
These European dandelions can be divided into two groups. The first group reproduces sexually, as do most seed plants. This group consists of dandelions that have a diploid set of chromosomes, and are sexually self-incompatible. Sexual reproduction involves a reduction of the somatic chromosome number by meiosis followed by a restoration of the somatic chromosome number by fertilisation. Diploid dandelions have eight pairs of chromosomes, and meiosis is regular with normal pairing of homologous chromosomes at the metaphase I stage of meiosis. The second group consists of polyploid (mostly triploid) apomicts, meaning that both a viable embryo as well as a functional endosperm is formed without prior fertilisation. In contrast to the sexual diploids, the pairing of chromosomes at metaphase I in triploid apomicts is strongly reduced. However pairing is still sufficient to allow some recombination between homologous chromosomes.
North American dandelions
The plants introduced to North America, originally as a food crop, are triploids that mainly reproduce by obligate gametophytic apomixis Though sexual dandelion plants are known in North America, almost all are clones that produce genetically identical seeds through apomixis. Some authorities recognise two subspecies of Taraxacum officinale, including:
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