Thorn is a short, sharp modified stem that grows out of the woody stems of many species of trees and shrubs. The honey locust, pyracantha shrub, and hawthorn are examples of plants that bear thorns. Thorns have a short growth period that ends with the formation of a sharp, hardened tip. The thorns protect the plant from damage by grazing animals. Plants with thorns are common in dry, warm areas, such as deserts and savannas.
Thorns are often confused with similar structures that grow from the stems of certain plants. The “thorns” of rose plants are better called prickles because they are simple outgrowths of the surface of the stem. The thornlike structures on such plants as black locust and barberry are actually modified leaves and should be called spines.
