What is a spine?
Spines are derived from leaves (either the entire leaf or some part of the leaf that has vascular bundles inside, like the petiole or a stipule). (2)
What is a spine NOT?
A spine is not a thorn. (1)
Resources
1. https://www.cactiguide.com/cactiornot/
2. https://en.wikipedia.org/wiki/Thorns,_spines,_and_prickles
