Our store manager, Dan Belfield, and I often have conversations about new items, cooking, dining, and the like. Dan has amassed a stunning amount of culinary wisdom (and is pleased to share it if you have a question, by the way), and we love testing each other and learning new things. It was this reason that I was so bewildered when he was unsure or what type of parsley to use for a particular cooking project. In my book, parsley knowledge is beginner stuff. But if Dan didn't know for sure, chances are that YOU don't either.
I'm going to set it straight for you, and it's easier to learn than you might have guessed: If you are cooking with it, use the flat parsley. Always. Curly parsley can be substituted, but any sensible cook knows that curly parsley is used primarily as a garnish and doesn't have any real flavor.
Flat parsley (the one you are supposed to be cooking with - are you paying attention?) may also be labeled as Italian parsley, and sometimes just plain parsley. To keep parsley fresh, store sprigs in the refrigerator with the stems in a jar of water covered with a plastic bag. Another way is to sprinkle the leaves with water, slip them into a plastic bag, and refrigerate. Both methods keep parsley fresh for around two weeks.
There is one more "parsley" I haven't mentioned, which isn't actually parsley at all: cilantro (or Chinese parsley). Cilantro has a very pungent smell and flavor and should never be used as a substitute for parsley. Be careful; it looks very similar to flat parsley. It's used mostly in Asian and Mexican dishes. Ever hear of coriander? Coriander is the fruit of the cilantro plant (which is then usually dried and ground up).