Term:

Prickle
Definition:

A sharp, pointed outgrowth of the epidermis of stems, leaves and other plant parts; e.g., on the trunk and branches of Ceiba pentandra (Bombacaceae) and Jacaratia spinosa (Caricaceae), on the stems of Smilax spp. (Smilacaceae), and on the stems and leaves of many species of Solanum.
Related Terms:

Spine
Thorn