This is not really a new vegetable, since it has been used since antiquity, but I was very surprised when I discovered that wild purslane (Portulace oleracea) grew aboundantly as a weed in my garden in Greece, I used to grow it from seeds as a vegetable i Norway.
It is said to contain more omega-3 fatty acids (alpha-linolenic acid in particular) than any other leafy vegetable plant, plus many vitamins, minerals and pigment types that are potent antioxidants. Besides that, it is also considered to be a beneficial companion plant, since they make a ground cover stabilizing moisture. And according to Pliny, it is advisable to wear the plant as an amulet to expel all evil, because of its haling properties. You can't ask for much more!