Finding out what this plant was took a few months. Finally, I was flipping through an edible plant book bought at a 2nd hand book store, and saw this mystery plant. The plant is Sheep Sorrel and is edible. Sheep sorrel has a tart kind of lemony taste to it. We now use it in our salads to give the salad a little flavor.
Sheep Sorrel is high in vitamins C and A. It has trace amounts of vitamin B and beneficial anti-oxidants. On the slightly negative side, Sheep Sorrel is high in oxalate acid. Therefore, it should not be eaten by the pound or else it will block the uptake of other important nutrients like calcium.