The differences between thorns, spines, and prickles on plants are as follows: Thorns are modified branches or stems arising from the axils of leaves, their main purpose being to protect the plant from grazing animals. For example, hawthorn trees have true thorns. Spines are modified leaves that harden, giving protection to the plant. For example, spines are found on most cactus plants. Prickles are sharp outgrowths from the outer layer (epidermis) of various plants, especially the leaves and stems. For example, raspberry canes often have prickles.