Apium graveolens var. rapaceum

Celeriac (Apium graveolens Rapaceum Group, synonyms Apium graveolens Celeriac Group and Apium graveolens var. rapaceum), also called celery root, knob celery, and turnip-rooted celery (although it is not a close relative of the turnip), is a group of cultivars of Apium graveolens cultivated for their edible bulb-like hypocotyl, and shoots. Celeriac is widely cultivated in the Mediterranean Basin and in Northern Europe. It is also but less commonly cultivated in North Africa, Siberia, Southwest Asia, and North America....read more on Wikipedia.