What is this Chinese ingredient called... in Chinese?

[Muban]

OK, I normally know these as Chinese Leaves:



There are a number of other names it is known as:

Nappa cabbage = celery cabbage = Chinese celery cabbage = Peking cabbage = Chinese cabbage = wong bok = petsai = shantung cabbage = hakusai = Chinese leaf (leaves) = michihli

Now I really like it and the Chinese I used to go to served it. But I tried to get it at one of the three Chineses near me - One couldn't do it (as the staff cooked it for themselves but don't have it on the menu so had ran out), the other two (whose english isn't as good) didn't know what I meant when I used the term 'Chinese Leaves'. So my question is what would a Chinese person know this ingredient as?! I might stand a chane of getting it somewhere if I knew what to ask for!

I have such a craving for this right now !!