Lime

Lime is an item found in Paper Mario. It can be obtained by going to the Dry Dry Desert's oasis and hitting the eastern (right side) tree with Mario's hammer. Leaving the Oasis area and returning will allow the player to collect another lime from the tree, and this may be done repeatedly. They restore three FP and can be cooked by Tayce T. to make a Tasty Tonic.

Star Piece sidequest
In one of Koopa Koot's favors, he says that he has been dragging his shell recently and want a "tart pick-me-up", for which he thinks a Lime should do the trick. If Mario brings him a Lime, he says, "Mmmmm... Yow! What a sour lime! That'll put a spring in my step", and rewards Mario with three Star Pieces.

Trivia

 * Limes are mentioned in Lumpy's diary in Paper Mario: The Thousand-Year Door, where he states that the last revision of his foodstuff during his Dry Dry Desert expedition consists of Lemons and Limes.