waggler is right. Several members of the carrot family are deadly poisonous, including water hemlock, poison hemlock, and fool's parsley, all of which have white flowers. I would never recommend eating wild carrots, or Queen Anne's Lace, unless you were to spend a lot of time studying plants. Another plant to avoid is water-parsnip (Sium sauve), which is perfectly edible, but looks too much like water hemlock. It only takes a mouthful of water hemlock to kill, so it's nothing to mess with.
Fortunately, wild parsnip (which TheAlmostIowaKid has in his photos) is pretty easy to distinguish from any poisonous plants. When it blooms it will have yellow flowers. Study the plant so you will be able to identifying it later without flowers, then come back in fall, winter, or early spring to dig the parsnips. The only inedible yellow-flowered plant that might be confused with wild parsnip is tansy, but tansy has rayless daisy like flowers, and does not have carrot-like roots.