Why Does a Cactus Have Spines?
First, let’s look at the spines of cactus for what they really are – the main part of cactus often functions as a modified stem and its spines are the leaves, they help to shade the surface of the cactus.
Of course, it may seem that the amount of shade that a single spine offers is questionable, but when you multiply them by the thousands, the amount of sun protection that they provide is substantial.
The prickly spines of a cactus prevent the plant from losing too much water. Plants are always losing water through their leaves. Plants with large leaves may lose many gallons a day. In the desert, where rain seldom falls, a plant with leaves would lose too much water and die.
So instead of growing large leaves, the cactus developed small spines, which are so thin that little water can escape through them. These sharp points help the cactus in another way, too. Few desert animals care to bite into a cactus, even though it is juicy. Another function that the spines serve is that they help certain species of cacti such as cholla to root and spread.
The spines of cholla are specially designed to detach and attach themselves to animals or people who happen to walk by too closely. There are tiny barbs at the tips which grab on to anything that gets too close. It almost appears as if they ‘jump’ off of the main cactus as they latch on the unlucky recipient.
The segments of cholla are then carried to another location where they eventually fall to the ground and then will root and grow into new cacti under ideal conditions. If you have ever seen cholla growing in large groups, this is why. Hopefully, you have a new appreciation for cacti and their spines. But, it’s still important to be careful because it hurts when you are pricked!