I’d like to briefly link to two great discussions about the origins of Taiwanese vegetable names:
There is apparently a popular theory that the word [高麗菜] (which a commenter renders as “Gao Li Cai”) derives from the name of Korea, but much more likely to me seems the idea that it’s a borrowing from a Germanic language (cf. English cole, German Kohl)…
And there is this older post about “A菜“ or “the ‘A’ vegetable” over at Doubting to Shuo, where it is generally agreed that it is of Hoklo (Taiwanese) origin.
Generally, when ordering dinner in Taiwan, one orders a “green vegetable” 青菜 and is given a choice between these two, as well as “cabbage mustard” 芥藍菜 (jièláncài), and a “water spinach” 空心菜 (kōngxīncài). The exact choice usually depends on what is fresh and in season. I’m good to go with any of them as they’re always tasty!