From the Super Mario Wiki
A Turtley Leaf is a special leaf used for tea that grows beside Mayor Kroop's house in Petalburg and could be found during the events of Paper Mario: The Thousand-Year Door. The leaves are often found trailing behind Koopa Troopas in gameplay. It restores three FP, but when mixed with other ingredients, it can help create a recipe that benefits the player even more.
Turtley Leaves appear to have replaced Koopa Leaves from the original Paper Mario, which served the same use.
Turtley Leaves reappear in Super Paper Mario with a much more useful ability: reducing damage taken by ½ for 10 seconds. Koopa Troopas (and related Koopa types) may drop them when defeated. Flimm also sells them at random.
Names in other languages
||Tartaruga (turtle) + foglia (leaf)