There are a lot of plants in the countryside that can hurt you. You can get tangled up in a patch of greenbrier or blackberry and swear you will never escape the vines with their needle-sharp prickles piercing the tender skin of your ankles and ripping holes in your favorite jeans. You find yourself circling carefully around a Washington hawthorn, attempting to evade its sharp, dangerous thorns, but nothing tops the pain of walking into the trunk of a Devil’s Walkingstick, sometimes called Hercules’ Club. You could swear that its deadly thorns have pierced you to the bone. And these are just a few plants that have evolved to bear sharp, pointy parts designed to repel invaders and inflict pain.

Have you ever thought about the definitions of prickles, spines, and thorns, or have you always figured they were just different words for the same pain-producing projections of unpleasant plants?

You might be surprised to learn that there are distinct differences be hand, grow from the de...