Why do roses have 'thorns'?

Plants have thorns to deter herbivores (animals that eat plants) from eating the leaves that the plant put so much energy into making. This type of defense is known as physical defense, because the plant physically defends against herbivores by poking them. Interestingly, rose thorns are not actually thorns. “Thorn” is used to describe a plant with branches modified for physical defense. Because the pointy projections of a rose bush are modified epidermal cells (similar to skin cells in humans), roses do not have thorns, they have prickles.