Amaranth, an annual flowering plant that propagates itself very readily and is one of the more widespread "food-secure" plants of the planet. Leaves are edible (delicious in stir fry) as well as the flowers--which are slightly bitter but good for you. We stir-fry the flowers with the leaves. You can also save the dried flower heads and get the seeds, which are a rich protein source.
We grow two kinds, including the irresistibly named Love Lies Bleeding (pictured) and they are a colorful addition to the garden. But they can take over, so be careful! Luckily, it's the kind of "weed" you can eat. Very drought-resistant and tough, and a pack of seeds for less than $2 can feed you virtually for the rest of your life.