Spines are sharp, pointed structures which are modified leaves. They give protection to the plants from herbivores. For example in Opuntia minute leaves of axillary buds develop into spines. In pineapple,(Annanas) and century plant(Agave), margins of the leaves are modified into spines. These are characteristic of xerophytes. Thorns are woody, straight and pointed structures. They give protection and help in climbing. Thorns are found in many plants such as Citrus, Canthium, Bougainvillea and Duranta. They are modified axillary buds. Thorns are endogenous(developing from internal tissues) while prickle as seen in rase are exogenous (developing from surface like epidermis).
Spines vs Thorns
|Spines are modification of leaves or part of leaves.||Thorns are modification of branches.|
|They occupy the same position as the leaves and bear a bud in their axil.||They are formed in the axil of the leaves in place of a bud.|
|Function include protection (defense) and also prevent excessive transpiration.||Function include protection (defense) and also serves as a climbing organ of the plant.|
|It does not so deeply seated and may not be connected with vascular tissues.||Deeply seated and has connection with vascular tissues.|
|Spines are exogenous in origin that is formed from tissues present externally.||Thorns are endogenous in origin that is formed from deeply seated tissues of the plant.|
|Example: Opuntia, Agave||Example: Carissa, Duranta|