From the Super Mario Wiki
The Strange Leaf is an item found in Paper Mario. It is a leaf from an unknown plant and looks like a simple green leaf. The Strange Leaf can be found by examining one of the bushes in front of Boo's Mansion in Forever Forest. It is one of the few leaf-based items in the Paper Mario series, along with the Koopa Leaf, Turtley Leaf, and Golden Leaf. When Mario uses this item, it will restore 5 Flower Points.
Delivering a Strange Leaf to Tayce T. in Toad Town and having her cook the item will turn the Strange Leaf into a Dizzy Dial. This may lead to the conclusion that Dizzy Dials are originally made from Strange Leaves.