Besides its uses as a healing herb as arona44 describes above, burdock roots, sprouts, and leaves are edible. Burdock (Arctium lappa) is a member of the parsley family along with carrots. The roots are long and thin with a dark brown coat and mildly sweet white flesh with a flavor similar to celery or artichoke. The young shoots and leaves from the plant are commonly eaten in salads or steamed. Burdock is especially popular in Japan, where it is called "gobo". It is commonly found in packaged fresh vegetable and salad mixes or deep fried like potatoes to make chips. It is also popular in mixed veggie tempura and dried as a snack.
There are two species of burdock, one that grows in Japan and one that grows wild in the United States. The plants can grow to be rather tall and generally have a reddish tinge. They are extremely hardy and grow in waysides and ditches along roads. Wild burdock from America can be harvested twice a year in the fall and spring. The Japanese species is generally harvested year-round. The skinny roots can either resemble firewood or ginseng root with its rootlets. Their length varies from one foot for the American variety to four feet for the Japanese types.
The best place to find burdock is in a well-stocked supermarket, farmer's market, or, your best bet, an Asian market. The roots will often come with a coating of dirt, but this can be easily washed off. Try to find firm, crisp looking roots. After purchasing, wrap them in a moistened paper towel and stick them in the fridge until you are ready to cook them. They will keep this way for several weeks.
Cooking the burdock root makes it tender and removes any bitterness. The skin of the burdock has the most flavor, so scrub it gently to remove all the dirt and reveal its rich brown color. Don't peel it. The stem, leaves, and hairy rootlets can be discarded. Also cut off the tip of the root if it is soft or discolored. After cutting the root into pieces, store them in water with a bit of lemon juice to prevent discoloring of the white flesh. The pieces can be steamed, boiled, or cooked in a stir-fry. They also are a nice addition to soups and stews. Burdock root can be used in place of parsnips, carrots, and artichoke hearts in some recipes. If you find young green leaves they can be steamed and have a flavor similar to asparagus.
Pregnant and lactating women should not eat burdock, as it contains a chemical that has been shown to cause contractions of the uterus.