thorn

plant anatomy

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Last updated

June 17, 2026

Quick Summary

A thorn is a sharp, rigid process on a plant, often a modified stem. Thorns serve as a defense mechanism against herbivores. While commonly referred to as thorns, roses actually have prickles, which are sharp protuberances from the plant's epidermis. Spines, another type of plant defense, are modified leaves or stipules, famously found on cacti, which also help shade the plant. Some plants, like stinging nettles, have trichomes, which are tiny, pointed structures that can inject poison.123

Other plant defense mechanisms include idioblasts (specialized cells containing defensive compounds), mutualism (where plants house and feed ants for protection), crypsis (camouflage), chemical signaling, and poisons. The term "thorn" can also refer to a woody plant with sharp structures, or metaphorically, something that causes distress.21

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angiosperm
Shoot system modifications
Thorns represent the modification of an axillary shoot system in which the leaves are reduced and die quickly and the stems are heavily sclerified and grow for only a limited time (determinate growth). Thorns appear to protect the plant against herbivores. Examples are found in…
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Thorns represent the modification of an axillary shoot system in which the leaves are reduced and die quickly and the stems are heavily sclerified and grow for only a limited time (determinate growth). Thorns appear to protect the plant against herbivores. Examples are found in…
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honey locust
…characteristically feature stout, sometimes branching thorns on the trunks and branches. The greenish unisexual flowers are typically inconspicuous and are borne in branching inflorescences (flower clusters). The legume fruits are ovate or elongated and are generally flattened; the beanlike seeds are usually surrounded by a sweet-tasting flesh.
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…characteristically feature stout, sometimes branching thorns on the trunks and branches. The greenish unisexual flowers are typically inconspicuous and are borne in branching inflorescences (flower clusters). The legume fruits are ovate or elongated and are generally flattened; the beanlike seeds are usually surrounded by a sweet-tasting flesh.
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