Spine

Spine, a leaf, or part of a leaf, modified into a pointed, hard, woody structure. The term is so often interchanged with thorn (q.v.) that it is perhaps better to speak specifically of a leaf-spine. In the thistles and hollies only the teeth of the leaves become spinous; in Robinia and most acacias, the stipules (q.v.); in some cases, the primary rachis or phyllopodium of a pinnate leaf after the fall of the leaflets; and in various barberries, marginal teeth or even the whole leaf. The spines of the Cactaceae are mostly leaf-structures. Spines differ from thorns in being lateral and from prickles in being continuous with the woody tissue of the branch or stem.