Thorns

Thorns are sharp, rigid plant outgrowths that commonly serve as a defense against herbivores and as a deterrent to browsing. In botanical terminology, a distinction is sometimes made between thorns, spines, and prickles: thorns are modified stems, spines are modified leaves or leaf parts, and prickles are outgrowths from the epidermis or cortex. In everyday use, the terms are often used loosely and the same plant may display multiple sharp structures.

Thorns occur on a variety of woody plants, including many trees and shrubs. They can be simple or branched, straight or curved, and may be located along trunks, branches, or twigs. Examples often cited in floras and field guides include the large paired thorns of honey locust and the stout thorns found on hawthorns. Some desert and tropical species possess thorny or spiny defenses that help reduce herbivory and survive in resource-limited environments.

Ecologically, thorns contribute to a plant’s defense strategy by increasing the physical barrier to grazing and by creating a less palatable or more difficult target for animals. In some plants, thorns are part of a broader suite of defensive traits that may include tough tissues, secondary metabolites, and spiny growth forms that reduce damage from herbivores and modify the surrounding microhabitat.

Humans interact with thorny plants in agriculture, horticulture, and landscaping. Thorns can deter animals and provide ecosystem services such as habitat structure, but they also pose handling hazards. Several ornamental and barrier species with thorny growth are cultivated for privacy, protection, or ornamental value.