Lemon

Lemons come off forest trees when you shake them, which is a slow trickle rather than a supply you can plan around. If you want a pile, walk a long stretch of forest and hit every trunk, because any single tree is unlikely to hand you one.

As food it is interchangeable with every other fruit, so eating one is rarely the point. The reason to hold a few is Shimmer. Fruit dropped in comes back as Ambrosia, which beats anything the raw ingredient gives you.

The tooltip is the first half of the old line about lemons and lemonade. The Lemonade item finishes the joke.