Polk Sallet tastes fantastic, it grows wild everywhere around here. I have never seen it for sale probably because it has to be picked and cooked (boiled three times) just right or could make you very sick. Never eat it raw in a salad. It's full of vitamins. Back when, it was one of the first greens to grow before the gardens produced. Everyone knew it would replenish your body with the vitamins not often available in winter foods. Here is a video how to harvest and cook it:
http://www.youtube.com/watch?v=_UYb3txLoh0