From the Super Mario Wiki
The Heart Plant is a species of plant that is found during the events of Paper Mario. It is a plant that has two leaves at the base, from which a brown question-mark-coiled stem stretches outward.
These plants grow all over Lavalava Island, especially deep in the Jade Jungle. Mario finds many of them during his search for the Baby Yoshis that have gotten lost in the jungle. When Mario touches one of them, they uncoil and drop a heart that restores 1 HP. What is interesting about them is that they have an infinite amount of hearts, so every time the player touches the plant, they give another heart, even if Mario is at full HP level.
However, the species is difficult to distinguish from the Hurt Plants that duplicate the looks of the Heart Plant. The only way to find out what plant it may be is to inspect and uncoil it. If it ends up being a Hurt Plant, Mario will have to battle it.
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