[Celtuce, Celery Lettuce, Asparagus Lettuce, Chinese Lettuce; Wosun, Woju (China); Lactuca sativa var asparagina alt var augustana, var angustata]
This lettuce is grown mainly for its stem, which is peeled and sliced or diced and used in stir fries. It is also often pickled. The flavor is fairly mild, much like a slightly bitter cucumber, so it's usually paired with stronger flavored items. The photo specimens were about 17 inches long (not counting leaves), 1.6 inches diameter and weighed about 8 ounces each. The form shown with a crown of leaves is how it is generally sold, but you'll notice the tip with the young more tender leaves has been removed. It is sold separately as A-Choy. The older leaves still attached are like Romaine leaves but tougher and more bitter, but they do stand up better to cooking. The Chinese do not eat raw greens for reasons you'd probably rather not dwell on.
More on Lettuce & Chicory
The photo to the left shows pickled stem lettuce, very common in Asian markets. It is pleasantly light and lightly crunchy, very easy to eat a whole jar at one sitting. Ingred: lettuce, sugar, soy sauce, water, msg.
Buying: Stem Lettuce can be found in most Asian produce markets, but tends to be seasonal. It's in good supply in late spring and early summer, spotty the rest of the year.
Storing: Loosely wrapped in plastic, and not wet, it should last up to two weeks in the fridge. The leaves may wither, but they're not the part you use.
Prep: Stem Lettuce has a very tough outer layer which must be removed. Use a regular swivel vegetable peeler (I greatly prefer the "Y" shaped form). The tough layer is lighter in color so you can usually see if it is sufficiently peeled or not. Otherwise test with a fingernail which should pierce the flesh easily. Note that the pithy white core in the high part of the stem does not ever become tender enough to chew, but has little substance. Remove it if practical, but if not it's small and easy to just swallow.
Cooking: Slices and cubes of stem lettuce are still "crisp tender" at 20 minutes of cooking. Depending on the texture you want, you may want to simmer them a bit before adding to a quickly cooked stir fry.