spine

noun

(L. spina: thorn, prickle) A stiff, hard, sharp-pointed plant structure on a plant, arising from below the epidermis, formed by the modification of a plant organ, as a leaf, leaf part, petiole, or stipule. The edge of the holly leaf is drawn out into spines, but in cacti the whole leaf is modified as a spine. Any structure with the appearance of a true spine. Cf. prickle, thorn.