Swiss chard is the same species as the beet, but bred to produce large tender leaves and colored stalks. As nutritious as spinach, it can be substituted in recipes calling for spinach. Stalks are edible and delicious, but need a bit longer to cook. The leaves need very little cooking.
Want to learn more? Look up Swiss Chard on Wikipedia.
STORE: In the fridge. Keep in a plastic bag or sealed container for maximum freshness.