Horsetail

In the original manual for Super Mario Bros, Bowser turned the citizens of the Mushroom Kingdon into Horsetail plants and Bricks.

In Paper Mario: The Thousand-Year Door, Horsetails are items that heal 3 HP.They are found in an area of Petal Meadows. Just before reaching the area with the bridge, coming from the Rogueport pipe, there is a Candy Cane that, when hit with a hammer, sinks down and bounces back up. After hitting the cane 10 times, a horsetail comes out. This can be done several times, after exiting and re-entering the area.

In Super Paper Mario, Horsetails are items that restore 7 HP and cures poison. They are usually dropped by Putrid Piranhas. They could also be bought in the Itty Bits in The Dotwood Tree for 18 coins.