Celtuce (Lactuca sativa var. asparagina, augustana, or angustata), also called stem lettuce, celery lettuce, asparagus lettuce, or Chinese lettuce, IPA (UK,US), is a cultivar of lettuce grown primarily for its thick stem, used as a vegetable. It is especially popular in China, and is called wosun or woju (although the latter name may also be used to mean lettuce in general). (source)