La Min 62 wrote:

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?

I believe "fish" can be plural but usually is treated as singular, depending on the context. 

John went to the lake yesterday and caught a lot of fish which filled a 5-gallon bucket.

In the lake, there were many types of fish, but not all the fishes are good for eating. Some are too bony.

For lattuce, I don't believe "s" is used for plural. People usually say "two heads of lattuce", not two lattuces.

I think the English language is changing in both directions myself.  We are creating new words as technology and human advances, but  bad “ English also takes root in under- privileged neighborhoods across the country. Saidly, it's even spoken among college students. The point I try to make is that incorrect English is used everyday by people and that’s ok.  But students should really avoid it.

With regards to vegetables, I think any veggie that resembles a sphere, like cauliflower, cabbage, or lettuce usually takes “a head of” to form the plural, correctly speaking. But I don't believe it's a rule.  If someone insists to say “two cabbages”, of course, chances are no one will point him out wrong.  It’s an interesting question though.  Come to think of it, I never gave it much thought before.  

Anonymous

“

Yes but not a single one of you has addressed his original question... He isn't talking about multiple heads of romaine or multiple heads of green leaf lettuce. He is talking about multiple heads of different types of lettuce. For instance, would it be better to say:

• "Fresh-cut Romaine and Iceberg lettuces must be rinsed..." or
  
• "Fresh-cut Romaine and Iceberg lettuce must be rinsed..."

”