Dandelions (aster-sunflower family) have spread through out the cooler parts of entire Northern Hemisphere. In the USA, humans consider dandelions a lawn nuisance. Curiously, though, dandelions don't appear on the short lists for USA invasive species. (Is it possible that they only invade that environmentalist's nightmare known as "the lawn", thus creating bio-diversity?) Further, dandelions are the delight of your non-human neighbors: leaf-munching rabbits, seed-eating birds, and pollen-collecting honeybees.
We've forgotten that early European settlers intentionally brought dandelions to North America because they're pure gold. So put down the evil weed poison and listen up.
Sources agree that dandelions are high in calcium, iron, potassium, phosphorus, sodium, and vitamins A, B, C and D. One web source even said that dandelion leaves are a better source of vitamin A than carrots. Dandelion root is said to be 40% inulin, a healthful plant fiber.
For The Monday Garden's "Eat An Invasive Plant Today" Club: Humans use dandelion, like its fellow-immigrant kin chicory, as a salad green, pot herb, and coffee substitute. The mature leaves are too bitter for good eating, but the young leaves are great in salad, soup or as a boiled vegetable. The root is collected in late summer when most bitter, then roasted and ground for coffee. Delicious sandwich: butter the bread, fill with fresh young leaves, and sprinkle with a little salt, pepper & lemon juice.
For centuries, humans have used dandelion products to treat a host of medical conditions including poor digestion, muscular pain, high blood pressure, constipation, warts, water retention, and heartburn. Indeed, the scientific name, taraxacum officinale, comes from the Greek words "taraxos", meaning "disorder", and "akos", meaning "remedy". The Arabs were using in 10th century; in India today, it's a specific for the liver. MotherNature.com sells it in capsules. The Japanese have used it in anti-cancer drug trials.
Dandelions also qualify as a Passover bitter herb. The milky sap of a Russian hybrid is reported to be used to make rubber. Other uses are suggested by some of its common names: cankerwort, bitterwort, swine snout, doonheadclock, Irish daisy, pu gong ying, and wild endive. It's said that "dandelion" comes from the French "dents de lion" due to the lion-teeth shape of the leaf.
Caution: Never eat any plant grown near a road or driveway. Heavy metals from car exhausts poison the ground and end up in the plants for decades. Ditto industrial sites and dumps. Also, some humans have dandelion allergies. Skin contact with the white milky sap should be avoided. Don't use except as a salad green without further reading, e.g. http://www.alternative-healthzine.com/html/0201_2.html and http://www.geocities.com/chadrx/dande.html