Purslane, a.k.a. "hogweed", "verdolaga", "pigweed", "pursley", and "moss rose" is an annual succulent which has a slightly sour and salty taste. The stems, leaves and flowers are all edible, and it can be eaten raw or cooked. I like to eat it raw.
Evidently, one of the easiest ways of acquiring Purslane is to buy a commercial bag of Peat Moss. The Purslane seeds will likely be present in the Peat Moss bag and will quickly sprout.
It grows mostly horizontally, creeping along the ground, which makes it pretty easy to identify. It's got red stems, succulent rounded green leaves and small yellow flowers.
Try it out.