I happened upon this site in my search as to whether or not one could ever add an "s" to the word lettuce. I understood the "countable" and "uncountable" aspects of the noun. However, these seem to refer to a one-kind/ head of lettuce. What if one is referring to a variety of lettuce(s), as in the varied types found as a planned mixture in salads?
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Comments  (Page 2) 
I just heard Michelle Obama say lettuces in reference to the new garden at the White House...can we call that relevant? 
Sounds fine to me.

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