Rhubarbs are not the most popular of vegetables, mostly because of their incredibly tart flavor. Moreover, rhubarbs can also be considered quite toxic when they are eaten in big quantities. Yet these incredibly rich leafy greens definitely pack a powerful punch. Amazingly, rhubarb has more calcium than one cup of milk, but, it doesn’t easily digest in the body. It also contains sennoside A, which is a bowel-stimulating property, also known as Senna, often used in popular herbal remedies as laxatives. While the plant itself cannot be eaten, the stalks are usually cut up and boiled, and used to flavor tarts, pies and other types of food.