Why Do Cacti Have Spines Instead of Leaves? (4 Reasons!)
We all know that cacti grow spines, but it’s rarely explained why they lack leaves. What if I told you this leafless feature of cacti—as well as cactus spines— is vital in keeping them alive?
Cacti spines are modified leaves that defend cacti from predators, help reduce water loss, harvest dew for extra moisture, and help with reproduction. These spines die once they have matured and do not contain any pores, ensuring the cacti does not lose excess water during photosynthesis.
In low rainfall environments, where most plants die before temperatures reach 113–122°F, hundreds of different cacti species flourish. But why is this? Find out the truth of the matter by reading on!
1. Protection Against Predators
Cacti have developed spines from regular leaves to protect themselves from herbivores. They may also grow barbed spines to make them more painful and difficult to dislodge, deterring predators.
Instead of growing leaves only to be consumed by hungry herbivores, many cacti have evolved to replace their leaves with spines all over their bodies—similar to porcupine quills.
These spines have evolved to develop barbs as well, and require significantly more effort to remove than non-barbed spines. Opuntia cacti are a good example of this and have many barbed spines.
Cactus spines are not poisonous. Once the spines have pierced the skin, however, they will snag into your skin and muscle, making them even more hard to remove. Even if they’re removed, some barbs will remain in the flesh.
A single cactus spine can get embedded so viciously, that it can lift a half-pound slab of meat!
On the bright side though, these barbed spines can also help cacti move to new places to grow, so keep reading to learn exactly how!
This system of defense works perfectly in protecting wild cacti and discouraging predators from attacking the plant repeatedly.
Read our article on “What Animals Eat Cactus?”
2. Reduce Water Loss
Unlike typical foliage, cactus spines are modified leaves that do not have pores or live tissue. Thus, spines are less likely to cause water loss in hot climates. Spines also reflect sunlight away from the cactus, reducing water loss.
Because normal leaves would transpire too much water in a tropical desert, the cactus has evolved to replace them with spines.
They might not look like it but cactus spines are highly modified leaves without stomata—also called pores—or even vascular tissue, a conducting plant tissue.
Since they don’t have stomata, the spines won’t lose any water and allow the cactus to store more water than they can with regular foliage.
Some cacti, like the golden barrel cactus, will grow hundreds of spines all over the central stem to help provide more shade.
Now, you might be asking, how do they photosynthesize?
Unlike other plants that produce light-catching pigments called chlorophyll inside their leaves, many cacti store their chlorophyll inside their central stems. Photosynthesis takes place in their succulent bodies. This is why cacti are green.
To further limit water loss, cactus spines will die once fully developed and become white. These white spines will reflect sunlight away from the stem and prevent sunburn.
When exposed to too much sun, the cactus will eventually turn red from sun stress.
Learn more in our article on the 3 reasons why cactus plants turn red.
3. Harvest Dew
The spines of cacti have microscopic grooves that direct dew and water droplets to cacti stems, where extra moisture is absorbed. This method of dew-harvesting helps many cacti survive in the desert.
Another reason why cacti develop spines instead of leaves is to harvest dew for extra moisture. The research only came out in 2015, so this is a less common feature of cactus spines that most people are not aware of.
Since the shortage of water is—unfortunately—becoming a global concern, scientists have been looking more into collecting water from dew and fogs. As a result, they were prompted to study cacti and their ability to survive dry and hot regions.
Timelapse snapshots show that dew droplets travel—sometimes against gravity—from the tips of the spines to the base of the cacti. When the water is fluorescent, it can be clearly seen moving inside the cactus stem.
If you think this is an incredibly fascinating find, you’re not alone!
Tapered microstructures were discovered on these cactus spines that help direct water droplets move from the spine to the areoles—unique bumps where spines grow from. Removing these spines also proved to significantly impact the plants’ ability to harvest dew.
So, along with cactus roots, spines also help cacti gather as much water as they can in extremely hot climates!
The spines of the copiapoa cinerea cactus proved to be the most efficient in collecting dew as another source of moisture.
4. Reproduce More Easily
Some cacti, such as the cholla cactus, use their barbed spines to attach themselves to passersby and reproduce in different areas. Broken cacti stems can grow into a new plant and produce more spines to continue propagating.
Earlier, I mentioned barbed spines. What’s even more interesting about them is that they aren’t just helpful in fending off hungry predators either. These spines can even help cacti reproduce!
The cholla cactus, also known as the jumping cholla, is a good example. It takes reproduction one step further by clinging to people and animals. This happens when spines pierce clothing and fur.
Many hikers have had their hikes ruined by this pesky cactus. Its spines purposefully cling to whatever brushes up against them. They allow external forces to break off a piece of the stem. Because of this, the cacti can spread to new areas.
When the cholla cactus stem finally falls to the ground, it will eventually develop roots and become an entirely new plant!
Some might consider the act of shedding numerous plant parts to create new growth too extreme. But if we’ve learned anything, it’s that most cacti aren’t afraid of taking drastic measures to survive.
Are There Any Cacti With Leaves?
Although rare, some cacti have regular leaves. The Pereskia cactus, for instance, is a non-succulent tree that grows traditional evergreen leaves. This cactus does not resemble other cacti but can be found growing spines and areoles on its stems.
You might say that some cacti species, like the queen of the night or the Christmas cactus, can be described as leafy plants. However, their “leaves” are usually just large, flat stems.
There are even some species, like the zig zag cactus, that do not grow any spines. However, there is a small group of cacti species that still produce leaves.
Pereskia cacti, also known as rose cactus, are commonly grown as ornamental plants and hedges.
Unlike other cacti, the Pereskia cactus grows as a tree and develops true leaves with laminas and petioles, or leaf blades and stems. But both have areoles and spines.
Areoles are the light-colored bumps on cacti that spines protrude from, a unique feature of cacti that makes them distinct from other plants, like succulents.
This cactus is originally from Venezuela, Paraguay, and is believed by scientists to be the original cactus all other cacti have evolved from. It might look like a normal tree but it’s part of the cactus family!
How to Handle a Cactus With Spines (When Repotting)
Spine-covered cacti must be handled carefully using thick leather gloves when repotting. Cover the spines with packaging peanuts and wrap the cacti with newspaper or a thick towel to ensure the spines do not make contact with the skin.
Cacti are pretty low maintenance so you probably won’t be handling it often unless you need to repot them or take it out of its pot to save it.
A thick pair of gloves will help prevent any cactus hair or needles from poking your skin. . Preferably, one with rubber or leather at the palm and fingertips.
Tongs can also be used to pick cacti up. But use this carefully. It might break the spines. Sure, your cactus might grow new spines but when they break, they will not grow back.
Learn more here in our test on “Do Cactus Spines Grow Back?”
You can also gently stuff packaging peanuts or styrofoam on the tips of the spines all around the cactus. This is a great way to add extra protection without buying any additional tools!
Thick towels or newspapers can also be wrapped around the cacti. In doing so, you can get a good grip on the cactus without puncturing yourself.
How to Remove Cactus Spines From Your Skin
Tweezers can remove and pull cactus spines out of the skin but must be used carefully to prevent further dislodgement. To extract small cactus hair, apply a thin layer of white Elmer’s glue on the wound and peel the dried glue off.
If you unfortunately got pricked while handling your cactus, don’t panic! Cactus owners have probably experienced this at least once while caring for cacti.
Larger spines can be carefully removed using a pair of tweezers or nose pliers. But be careful not to apply too much pressure, as you might break the spines off and leave an even smaller piece embedded in your finger.
For hair-like bristles you can’t see, check if you have any white Elmer’s glue handy.
White Elmer’s glue has helped hundreds of cactus owners for years in removing cactus hair. Apply a thin layer of glue on the area with hair, let it dry, and gently peel it off.
You can repeat this process over and over until all spines have been completely extracted.
But self-removal is not always effective and can cause severe pain and inflammation. If you’re still experiencing pain after several hours, seek medical assistance.
FAQs
Are barrel cactus thorns poisonous?
Cactus spines do not contain any toxins and are not poisonous. They can, however, cause bleeding and increase the risk of infection by allowing bacteria to enter the punctured skin. Severe injuries must always be treated by medical authorities to prevent inflammation and extreme pain.
Are cactus spines seeds?
Although cactus spines can help the plant reproduce by catching onto animals and humans and spreading to different areas, cactus spines are not seeds. The seeds of cacti can be found inside cactus fruit and are typically round and flat. Cactus seeds are difficult to raise and take many months to germinate.
Summary of Why Cactus Have Spines Instead of Leaves
Instead of growing wide flat leaves that make excess water evaporate in heat, most cacti have developed modified leaves called spines. These help reduce water loss, harvest dew, and defend against hungry predators. Barbed cactus spines also aid with propagation.
Spiny cactus can be grown at home. But repotting be done carefully with thick gloves and moved with towels or newspapers covering the spines to prevent contact. Remove embedded cactus spines from the flesh by pulling them out with a pair of tweezers or peeling it out with a layer of white glue.
Sources
- “Cacti and succulents” by Deborah L. Brown in University of Minnesota
- “Cactus Spines” by James D. Mauseth in University of Texas
- “Modifications to Cactus Leaves” by James D. Mauseth in University of Texas
- “Pereskia” by n/a in NC State University
- “Cactus Spine Wounds: A Case Report and Short Review of the Literature” by Raymond A Dieter Jr, Lisa R Whitehouse, and Rebecca Gulliver in National Center for Biotechnology Information
- “Hierarchical structures of cactus spines that aid in the directional movement of dew droplets” by F. T. Malik, R. M. Clement, D. T. Gethin, M. Kiernan, T. Goral, P. Griffiths, D. Beynon, and A. R. Parker in National Center for Biotechnology Information
