Celery is a ubiquitous ingredient in American cookery, near and dear to many home cooks, but celeriac (also known as celery root) is only just coming into its own here. While their appearances are wildly different, celery and celery root are very closely related botanically. Does this mean they can be used interchangeably in cooking?
The short answer is no. Celery and celeriac are basically the same plant, Apium graveolens, with celeriac being a variety cultivated for its root rather than for its stalks (var. rapaceum). They both have the taste of celery, although many people find celeriac to be earthier and more intense. Both can be used either cooked or raw, but in either case, their texture is widely different, so they are not interchangeable in most recipes.
So, What Is Celery?
Celery comes in stalks loosely clustered into a head. It is a bright-green, crunchy, full-flavored vegetable and can be used in dozens of ways, both raw and cooked. Many people would not consider their kitchen well-stocked without at least a few stalks of celery on hand. It is high in sodium and water, making it a refreshing, bright, and versatile addition to soups, stocks, and salads.
On the other hand, celeriac is a pale-yellow, dense, knobby (some say even ugly) root; it's roughly the size and shape of a grapefruit. Like most root vegetables, celeriac is excellent in stews and soups, and makes a perfect a gratin — with or without the addition of potato. It also makes an amazingly silky purée. Left raw, it can be grated into salads, as is the case in its most well-known dish, céléri remoulade.
It requires a fair amount of peeling to reveal its creamy-colored flesh. To peel, simply lop off the top and bottom so that it sits flat on your cutting board and work your knife down the sides to remove the knobs and roots. Occasionally you may have to take out a few rougher spots with a sturdy peeler. Use the flesh right away or put it in acidulated water to prevent discoloration.