The influence of cactus spine surface structure on puncture performance and anchoring ability is tuned for ecology

Spines are common morphological features found in almost all major biological groups offering an opportunity to explore large-scale evolutionary convergence across disparate clades. As an example, opuntioid cacti have spines with barbed ornamentation that is remarkably similar in form and scale to that found on porcupine quills, suggesting specific biomechanical convergence across the animal and plant kingdoms. While the mechanics of porcupine quills as defensive mechanisms has been previously tested, the mechanics of cacti spines (which have evolved to fill a number of functions including defense, climbing and dispersal) has not been characterized. Here we study the puncturing and anchoring ability of six species of cactus, including both barbed and non-barbed spines. We found that barbed spines require less work to puncture a variety of targets than non-barbed spines. Barbed spines also require more work than non-barbed spines to withdraw from biological materials, due to their barbs...