This delicate green, in season in spring and fall, is slightly spicy and a rich source of protein, vitamin B6, niacin, thiamine, pantothenic acid, zinc, vitamin C, calcium, folate, magnesium, and potassium. It will keep for about a week in the fridge. Like other bitter greens, including escarole, watercress, dandelion and rabe, arugula is said to aid the liver in its work metabolizing fat and protein.