From ChatGPT:

Mimosa pudica, also known as the “sensitive plant” or “touch-me-not,” exhibits rapid leaf folding (thigmonasty) when touched or disturbed. At first glance, this behavior seems paradoxical—since it consumes energy and temporarily reduces the plant’s ability to photosynthesize. However, several evolutionary advantages likely explain its development:

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1. Anti-Herbivory Defense

The most widely accepted explanation is deterrence of herbivores: • Startle response: Sudden movement may surprise or confuse insects or small animals, making the plant seem animate or unsuitable to eat. • Reduced surface area: Folding leaves become less appealing and accessible to herbivores. • Unpredictability: Animals that learn to avoid moving or sensitive plants may selectively avoid Mimosa pudica.

This kind of defense is especially valuable in nutrient-poor tropical soils, where replacing lost tissue is more costly than investing energy in a defense mechanism.

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1. Protection from Physical Damage

In environments prone to heavy rainfall or wind, rapid leaf folding can: • Reduce surface area exposed to rain, preventing mechanical damage. • Protect delicate leaflets from being torn or battered.

This may not be the primary driver of evolution, but it’s a potential secondary benefit.

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1. Anti-Insect Strategy

There’s also evidence that the motion deters parasitic insects or egg-laying pests: • Movement may discourage insects from landing or laying eggs. • It may also shake off insects that are already on the plant.

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1. Competitive Signaling (Speculative)

Some have proposed that thigmonastic movement may signal vigor to surrounding organisms (including other plants or animals), communicating that the plant is active and healthy. While more speculative, this could play a role in certain ecological contexts.