Are these greens 苦木？
I don't cook much.

This looks like 油麦菜.

It is a variation of lettuce (Lactuca sativa). From a search on the web (wikipedia), I don't think there is a specific English name for it.

百度百科 gives a Latin name "Lactuca sativa var longifoliaf. Lam" for it. The site also says it can be called "莜麦菜", "苦菜" or "生菜" (note: there is also another kind of vegetable called "生菜"). But I've never heard anyone calling it "苦木". And as it is a kind of vegetable, I think it should be unlikely for it to be called "苦木".