Why do thorns grow on certain plants?

Thorns are essentially defense mechanisms for the plant, much like teeth are for an animal. The sharp points protect the plant against animals that want to eat it. Honey locust trees are a prime example of plants with thorns. Thorns are actually a type of branch, and roses do not have true thorns. read more

Thorns are actually a type of branch, and roses do not have true thorns. Instead, roses have prickles, which are a part of the skin of the plant. Cacti, on the other hand, have spines, which are a modified leaf. read more

In plant morphology, thorns, spines, and prickles, and in general spinose structures (sometimes called spinose teeth or spinose apical processes), are hard, rigid extensions or modifications of leaves, roots, stems or buds with sharp, stiff ends, and generally serve the same function: physically deterring animals from eating the plant material. read more