Going Underground

All root vegetables grow underground, but not all vegetables that grow underground are roots. The difference is basically horticultural, but in the interest of culinary correctness, parsnips, radishes, turnips, rutabagas, carrots and beets are root vegetables. Potatoes (both sweet and white) are tubers--the swollen tips of underground stems. So are water chestnuts, by the way. Many edible members of the lily family--onions, garlic, leeks and shallots--are actually swollen stems that grow underground as well.