Petuni

Petuni is Punio's little sister in Paper Mario: The Thousand-Year Door. She eventually needs rescuing from Punio and Mario and can be easily rescued with a key, then she will proceed with giving Punio a dried shroom she had been saving him. Other than that, she hasn't the most activity within the game, but plays a fair part of importance to Punio's well-being.

Other things
Mario can play "stump Petuni." Say "Mario likes which person the most?" She will say Princess Peach and will give you a Mystic Egg.

Petuni participates in the '100 puni group' that helps Mario through the great tree, though she cannot always be seen in the group for an unknown reason or glitch.