response: Oh, well it's commonly used as a salad green.
original_response: Yes that is why it is a common salad green, and is the usual lettuce used in Caesar salad.
history: I do not care for romaine lettuce at all. Oh?  Did you know it's tolerant of heat though, unlike most lettuces? I just have never cared for romaine lettuce. Something about the taste. I was not aware it was tolerant of heat. Do you know anything else interesting about it? Well, you know that fine-bitter herb flavour it has?  It's because of the milky fluid in the thick ribs. I was not aware that is where it got the bitter taste but I think that is what I do not like. I do know that it is the usual lettuce used in Caesar salad. That is about all I know about romaine lettuce. Well I can tell you that the bitter taste is especially found on the ribs of the outer leaves, which are older. Hmm good to know.  What's it used for mostly?
knowledge: Romaine is a common salad green, and is the usual lettuce used in Caesar salad.