I tried to reply over there but didn't see how. Portulaca oleracea, Oron's suggestion is used a lot in summer salads here in Greece, usually in tomato salads instead of cucumber (it has the same crunchy texture). It should be cut before flowering. Interestingly enough it grows mostly in tomato (and other summer vegetable beds) as a weed (or self-seeder) because it likes the aerated soil, manure, water and attention. It is also eaten pickled (the early shoots or tender tips). I have used individual leaves to add texture to stir-fries.