Over time, those leaves evolved into the spiky spines we see on cactuses today because they help the plants survive in hot, dry environments. "They can be a defense mechanism to discourage herbivores - animals that eat plants - from eating the cactus. But, also, spines create shade!" explains Kimberlie McCue.

What is the purpose of thorns on a cactus?

By shading the cactus, these spines also help prevent the cactus from losing water through evaporation. So all in all, spines are adaptations that protect and help cacti hide from animals that may want to eat them. They also provide shade for the plant, which keeps them cooler and limits water loss.

Why do cactus have thorns instead of leaves?

cactus have spines instead of leaves to prevent a loss of water from the surface of the leaf. Cactus has spines rather than leaves so as to save water.