What vegetable has a dark root with hot sharp taste?

The vegetable you're thinking of is most likely wasabi.

Here's why:

* Dark root: Wasabi is a root vegetable with a dark green to dark brown color.

* Hot, sharp taste: Wasabi is known for its intense, pungent flavor that is both hot and sharp, similar to horseradish.

Let me know if you have any other clues!