The Touch Me Not plant is a member of the Mimosa genus, which is known for its sensitive leaves that fold in when touched.
It’s thought that this defense mechanism evolved to protect the plants from herbivores. When an animal or person brushes against the leaves, they cause a mechanical stimulation that triggers an electrical signal in the plant. This signal causes the leaves to fold up and close, making it more difficult for the herbivore to eat them.
While this may seem like a quick way to escape being eaten, it takes quite a bit of energy for the plant to close its leaves. So, it’s only used as a last resort when other methods of deterring herbivores (like thorns or chemicals) have failed.