celeriac, (subspecies Apium graveolens, variety rapaceum), type of celery (Apium graveolens, variety rapaceum) grown for its knobby edible hypocotyl (stem), which is used as a raw or cooked vegetable. Originally cultivated in the Mediterranean and in northern Europe, it was introduced into Britain in the 18th century.
Celeriac may be harvested when immature, when its flavour is more intense, or when the hypocotyl reaches a size of roughly 12 cm (4.7 inches). It can be prepared in various ways, including by blanching or roasting, and it may be mashed. It commonly is used in savory dishes, including casseroles, and its leaves may be used as a garnish.