Why Do Cactus Have Spines ?

The first thing most people think of when they think of cactus are their spines.  They can be inconvenient and painful, (especially when you are a horticulturist who happens to work in desert gardens).  However, there are actually very important reasons that cacti have spines and not all of them are obvious....

Golden Barrel Cactus (Echinocactus grusonii) 

Cactus spines are actually modified leaves.  It helps if you think of cactus as a large stem with leaves (spines).  One of the main functions of the spines is fairly obvious, which is to protect cacti from predators such as animals and people.  Spines will turn away most animals, but there are a few that are not put off by prickly spines.  These animals include javelina, pack rats, desert tortoises and even Desert Bighorn sheep.

 Saguaro  (Carnegiea gigantea)

 

A major function of cactus spines serve to provide protection for the cactus from the sun.  At first, it is hard to believe that tiny cactus spines offer any real protection from the intense desert sun.  But when you consider that a cactus can have thousands of spines and each spine provides a small amount of shade and multiply that by 1,000 - well it becomes easier to believe that spines really do offer some protection from the sun for the skin of the cactus.

Teddy Bear Cholla (Opuntia bigelovii)  

For some species of Cholla cacti, their spines serve an additional purpose.  Cholla spines are vital to their propagation.   They have tiny barbs at their tips which are very sensitive to movement.  This causes the segments of the cholla  to "jump out" and attach themselves to whatever walks by.  They do not actually "jump", but their spines are very sensitive to movement and will quickly adhere to whatever walks by - human or animal.  When the detached stem segments fall to the ground, they will then root in the soil.  This is the main reason you often find Cholla growing in large groups.

**If you find a piece of Cholla embedded in your clothes or worse, your skin - you can use a comb to help pull out the barbs.  It is painful, I once had one embedded in my leg.  When hiking in the desert, it is easy to get them stuck on your shoes.  I usually grab a rock and use it to take off the Cholla segment.  When all else fails, a good pair of needle-nose pliers works.

 

Hedgehog Cactus (Echinocereus engelmannii)

  So next time you find yourself around a cactus, be careful, but also take time to marvel at how their prickly spines help protect them from predators and the elements as well as assist in propagation for certain cacti species.