Yesterday on one of the potted plants, my wife discovers some dandelions. I was quite interested in looking at the small yellow wild flowers that grew out from two plants with zig-zag leaves. Actually they did not belong to the family of flowers which was planned for display on our nearby footbridge. The flowers of the dandelions are the composite flower head (see the first and second photo) consisting of many flowers called florets. Dandelions are found in Africa, Asia and Europe. Many of its species have asexual reproduction so that seeds can be produced without pollination.
Dandelions are tap-rooted, biennial (二年生)or perennial (多年生) herbaceous plants (草本植物) living in temperate areas of our Northern Hemisphere. They are commonly known as weeds (野草) or ruderals.
The leaves of dandelions (see the third photo) 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, which kills those plants by cutting off their access to sunlight. It is strange to find a bright yellow flower head, which is open in the daytime but closes at night. It 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 head matures into a spherical "clock" (also known as a "wishie") containing many single-seeded fruits (achenes). Each achene is attached to a pappus of fine white hairs, which enable wind-aided dispersal over long distances.
Away from their native regions, dandelions have become established in the Americas, Australia, and New Zealand, and are now common throughout all temperate regions. In this manner, it is world-wide.
The flower head (see the first and second photo) 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 a beak, which elongates as the fruit matures. The beak breaks off from the achene quite easily. After pollination, the dandelion flower dries out for about 1-2 days and then the seed-bearing parachutes expand and lift out of the dried flower head. The dried part of the flower drops off and the parachute ball (see the ball-like one at the bottom of the first photo) opens into a full sphere. The parachute drops off when the seed strikes an obstacle. Often dandelions can be observed growing in a crevice near a wall, because the blowing fruits hit the wall and the feathery pappi drop off, sending the dandelion seeds to the base of the obstacle where they germinate. After the seed is released, the parachutes lose their feathered structure and take on a fuzzy, cotton-like appearance, often called "dandelion snow." While it was probably not developed evolutionarily, Dandelions seeds are often dispersed by young children, who often blow on or kick the clock.
There are usually 54 to 172 seeds produced per head, but a single plant can produce more than 2000 seeds a year.
Dandelions are considered as a kind of medicinal herb. They are grown commercially on a small scale as a leaf vegetable. The leaves (called dandelion greens closest in character to mustard greens) can be eaten cooked or raw in various forms, such as in soup or salad. 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, The leaves are high in Vitamin A, Vitamin C and iron, carrying more iron and calcium than spinach.
Dandelion flowers can be used to make dandelion wine, for which there are many recipes. It has been used in a saison ale called Pissenlit (literally “wet the bed” in French) made by Brasserie Fantome in Belgium. Another recipe using the plant is dandelion flower jam. Ground roasted dandelion root can be used as a coffee substitute. Dandelion root is a registered drug in Canada, sold principally as a diuretic. A leaf decoction can be drunk to “purify the blood”, for the treatment of anemia, jaundice, and also for nervousness. Drunk before meals, dandelion root coffee is claimed to stimulate digestive functions and function as a liver tonic. “Dandelion and Burdock” is a soft drink that has long been popular in the United Kingdom with authentic recipes sold by health food shops.
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.
Yellow or green dye colours can be obtained from the flowers but little colour can be obtained from the roots of the plant.
Dandelions are important plants for bees. Not only is the appearance of their flowers used as an indicator that the honey bee season is starting, but they are also an important source of nectar and pollen early in the season.
I am deeply impressed after reading the materials from Wikipedia (source) that Dandelions are so useful to mankind.