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. More on managing this plant below the "add to cart" button.
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.
Other people put it in a permanent place, usually with shrubs and perennials so they don't have to work around it in their vegetable beds.
You will get the most (and the most tender) leaves if you keep cutting it, taking the largest leaves for use, and leaving 4-6 leaves on the plant to regrow. Clip off the flower stalks as they form, unless you are growing it as a bee plant. If you leave the flower stalks, it will make lots of little yellow mustard-type flowers in summer, followed by seeds. It self-sows vigorously. If you are going to let it flower and make seed, be sure to put it in it's own space where you won't mind little seedlings.