What’s the healthiest vegetable on the planet? If you said kale, you would be wrong. According to research published by the U.S. Centers for Disease Control’s journal Preventing Chronic Disease, the true powerhouse vegetable is watercress, a cruciferous cousin of kale that grows in fresh spring water and adds a peppery punch to salads. Use spicy watercress raw in smoothies or sandwiches for a good-for-you boost. Other ideas: Gently cook the greens as you would spinach, or try this simple salad of watercress and macadamia nuts from celebrity chef Ming Tsai. Check out these 12 delicious superfoods that will boost your diet.