Celeriac is the white round part of the celery root.

块根芹是一种白色圆形的芹菜根。

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Also known as celery root, knob celery and turnip-rooted celery, celeriac developed from the same wild species as did stalk celery.

NPR: The Vegetable World's Ugly Duckling: Celeriac

Celeriac is a celery variety refined over time to produce an increasingly large, solid, globular root just below the soil surface.

NPR: The Vegetable World's Ugly Duckling: Celeriac