From the Super Mario Wiki
Posie is a flower that lives in Flower Fields during the events of Paper Mario. She lives under the Crystal Tree, a tree that produces Crystal Berries. Posie is very protective of the Crystal Tree. She provides Mario with the Fertile Soil needed to reach Cloudy Climb.
The Crystal Tree's roots are connected to Posie's roots, so if Mario whacks the tree with his Hammer, Posie will feel hurt. Although Posie requests that Mario refrain from hitting the tree, she's willing to shake a Crystal Berry free for him when he asks for one to give to Rosie.
If Mario hits her tree too many times, Posie will throw Mario out of her part of section of Flower Fields. If Mario walks back in, Posie will scream at him to get out immediately. This banning will not prove permanent, however; if Mario returns to her area five times and she'll eventually cave in. However, if Mario keeps hitting her tree, she'll keep kicking the plumber out an infinite number of times.
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