Dandelion (AKA Taraxacum)

## Introduction

***Taraxacum*** (/təˈræksəkəm/) is a large 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 is native to Eurasia and North America, but the two most commonplace species worldwide, *T. officinale* (the common dandelion) and *T. erythrospermum* (the red-seeded dandelion), were introduced from Europe into North America, where they now propagate as wildflowers. Both species are edible in their entirety. The common name *dandelion* (/ˈdændəlaɪ.ən/ *DAN-də-ly-ən*; from French *dent-de-lion* 'lion's tooth') is also given to specific members of the genus.

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.

In general, the leaves are 50–250 mm (2–10 in) long or longer, simple, lobed-to-pinnatisect, 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 10–100 mm (3⁄8–3+7⁄8 in) or more 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 20–50 mm (3⁄4–2 in) in diameter and consist entirely of ray florets. The flower heads mature into spherical seed heads sometimes called *blowballs* or *clocks* (in both British and American English) 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.[*citation needed*]

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*. 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.[*citation needed*]

## Description

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 (i.e. morphologically distinct clonal populations) are recognised in nine loosely defined sections, of which 40 are "probably endemic". 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 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.
The pappus of a dandelion seed, which aids in wind-driven dispersal
Field with flowering dandelions, Tatarstan, Russia

## Similar plants

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 cat's ears are coarsely hairy.[*citation needed*]

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.

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.[*citation needed*]

## Classification

The genus is taxonomically complex due to the presence of apomixis: any morphologically distinct clonal population would deserve its own microspecies. Phylogenetic approaches are also complicated by the accelerated mutation in apomixic lines and repeated ancient hybridization events in the genus.

As of 1970, the group is divided into about 34 macrospecies or sections, and about 2000 microspecies; some botanists take a much narrower view and only accept a total of about 60 (macro)species. By 2015, the number has been revised to include 60 sections and about 2800 microspecies. 30 of these sections are known to reproduce sexually.

About 235 apomictic and polyploid microspecies have been recorded in Great Britain and Ireland alone.

I obtained this from Wikipedia.