Arugula

a Mediterranean plant, Eruca vesicaria sativa, of the mustard family, having pungent leaves used in salads.
Contemporary Examples

Papaya and arugula Salad by Anne Byrn The Dinner Doctor offers a salad to please both the palate and the eye.
What to Eat Cookstr.com July 27, 2009

Serve the burgers in toasted pita bread with lots of arugula, thinly sliced red onions, and roasted red peppers.
Foods That We Love But Shouldn’t Lydia Brownlow July 14, 2011

With the heartland hungry for a different kind of change, Pence is the conservative antidote to arugula.
Sarah Palin’s Newest Rival Mark McKinnon October 26, 2010

Serve in warm pita bread with arugula, roasted red pepper, sliced red onion, and the following salsa.
Foods That We Love But Shouldn’t Lydia Brownlow July 14, 2011

Toss together the radicchio, arugula, apple and pumpkin seeds in a medium bowl.
Divine Apple Dishes Anne Burrell January 5, 2011

At the checkout, her total for bananas, arugula, blackberries, kale, yogurt, rice noodles, and tofu comes to $34.21.
The Gluten-Free Diet Has Two Faces Andrea Powell May 5, 2014

noun
another name for rocket2 (sense 2)
n.

edible cruciform plant (Eruca sativa) used originally in the Mediterranean region as a salad; the American English and Australian form of the name is (via Italian immigrants) from dialectal variant of Italian ruchetta, a diminutive form of ruca-, from Latin eruca, a name of some cabbage-like plant, from PIE *gher(s)-uka-, from root *ghers- “to bristle” (see horror).

In England, the usual name is rocket (see rocket (n.1)), which is from Italian ruchetta via French roquette. It also sometimes is called hedge mustard.