In botanical morphology, thorns, spines, and prickles are hard structures with sharp, or at least pointed, ends. In spite of this common feature, they differ in their growth and development on the plant; they are modified versions of different plant organs, stems, stipules, leaf veins, or hairs. In nontechnical usage, the terms may be synonymous.

Spinescent is a term used for plants that have sharp structures, but these are not necessarily spines in the technical sense.

Some authors prefer not to distinguish spines from thorns because, like thorns, and unlike prickles, they commonly contain vascular tissue.

Many plants commonly thought of as having thorns or spines actually have prickles. Roses, for instance, have prickles.