Perennial Arugula, Rucola selvatica, Wild Rocket "Sylvetta
Perennial, and very heat-resistant arugula. Different species (Diplotaxis erucoides), same nutty, spicy flavor. A wild form of arugula, with very deeply lobed dark green narrow leaves. Hardy plants are not as fast-growing as annual arugula, but grow steadily, reaching 3" in 3 weeks. Doesn't need great soil or full sun. Keep cutting and watering regularly for best flavor. Very deep-rooted--put this in a permanent bed, and cut regularly for salads. Leave a plant or two to make flowers--this is more loved by honeybees than anything I've ever grown. You can hear them the length of the garden. Self-sows strongly (and stops making new leaves) if you leave the flower stalks to make seedpods, so cut them off.
Will die back with freezing, and re-sprout quickly in spring. (Annual arugula, will stay greener in colder weather, but doesn't come back. It's also less heat resistant.) This perennial arugula really shines as an extra-early crop, and as a spicy addition to salads all through the summer. Native to the Mediterranean; hardy to about zone 5, depending on drainage. Can be overwintered in a pot, or used as a winter greenhouse crop also.
I have only lately realized how terrific this is lightly cooked. You can throw it into a pot of spaghetti a couple of minutes before the end of cooking, drain it along with the spaghetti, toss with some cheese and maybe olives or capers, and the meal is ready.