This might be hard to describe. But I am trying to get healthy and eat more salads, and I have been buying lettuce mixes. But there is one type that of lettuce leaf that is only in very few mixes, and very little of it there. And I hate it, I want to know what it is so I can avoid those mixes.
the only way I can describe it is tasting very strongly like fertile(Manurey, composty) dirt smells afters it’s been rained on.
I don’t know what it looks like. There is never very much, I just get the taste after having put an assorted forkful in my mouth and start chewing, and don’t really want to do forensic analysis on it at that point.
And I have never found any for as long as I have the patience after that to eat one leaf at a time.
Can you at least tell us what brand of mixed greens you buy? If you can’t identify it by sight, I’m not sure what to tell you - if you can give me a brand, I can tell you what’s in them and what it MIGHT be.
Some bagged prepared salads are sold as pre-washed, but it could be just about anything - as the OP only tastes it when shovelling leaves indiscriminately - it could be dirt, bugs, weeds, rotten leaves, or assorted other contaminants. Or some leaf in the mix. I don’t see how we can factually answer such a vaguely-defined question.
You’ve described beet greens, which are a rounded leaf with a red central vein. Lots of people liken the taste of beets and beet greens to dirt or earth. Here’s a photo of a beet leaf in a salad mix: