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.
Leaf celery or cutting celery (Apium graveolens var. secalinum): this type of celery is grown for its leaves, and is used as an herb in Europe and China; typically the only place to buy it in the US is Asian and farmers’ markets. Leaf celery is closely related to wild celery, and is also known as smallage, cutting celery, or Chinese celery.