Spinescence

Though the words are often used interchangeably, thorns, spines, and prickles are botanically distinct structures. They are labeled based on which part of the plant they originate from.

Thorns are modified stems or branches. Like stems, they are still connected to the plant’s vascular system—its circulatory system. In some plants, leaves can still grow off of a thorn as if it were a normal stem.

Spines are modified leaves or leaf parts. Like thorns, they are usually connected to the plant’s vascular system. The spine may take the place of the stipules (small growth at the base of the leaf) or the entire leaf itself.