I visited a Cambodian supermarket in MA for the first time last week. It has seen better days, apparently on the decline since an H-Mart opened 30 minutes away. I bought something packaged as "baby shing hai" because there was a lot of it, and most of their other greens looked past their prime. These are 5-9" long heads of white, celery-ish looking stalks that taper to a single, smooth-edged dark green leaf at the end of each stalk. The leaves are the texture and thickness of the outer leaves of a head of romaine. The flavor is mild, perhaps a teeny bit bitter. I sliced it crosswise and sauteed it with garlic and shallots, then added a splash of teriyaki sauce.
Is this just a different name for bok choy? Googling and searching CH got me nowhere.