Thorn
/θɔrn/
Definition
Thorn refers to a sharp, rigid, pointed plant structure formed from a modified stem or branch. Unlike prickles, which come from the outer skin, or spines, which are modified leaves or leaf parts, thorn is woody and connected to the plant’s internal vascular tissue that carries water and nutrients. It usually functions as protection against animals and is found on some trees and shrubs, such as hawthorn and citrus.
Function in Plants
- Defense against browsing: A thorn helps reduce damage from grazing animals by making stems harder to bite or strip, which can protect buds and young shoots.
- Clue to plant identity: Its presence, position, and branching pattern can help distinguish species or genera, especially in groups where similar leaves or flowers make identification harder.
- Modified stem origin: Because a thorn develops from stem tissue, it is connected to the plant’s vascular system, the transport tissue that moves water and sugars.
- Handling and placement: In gardens, a thorn affects where a plant is placed and how it is pruned or propagated, since stems may be harder to tie, cut, or move safely.
Related Terms
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Branch
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Node
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Leaf
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Woody plant
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