Of Spines, Thorns and Things that Poke in the Night

by Ron Harton

The desert seems to have more than its share of plants with spines and thorns. Pacific Crest Trail hikers, who begin on the Mexican border near Campo, California, and traverse the length of three states to reach Canada, complain frequently about the desert portion of the trail. One hiker, writing on the online PCT news list, said that everything in the desert poked and stuck her. She just couldn’t wait until she left the desert behind and reached the “softer” forest.

An early Jesuit explorer, Johann Jakob Baegert, felt the same way. He said of the lower California desert, “Thorns…are especially numerous, and there are many of frightening aspect. It seems as if the curse of the Lord, laid upon the earth after the fall of Adam, fell especially hard on California and had its effect.”

Why Spines?

Although it may not matter much to you when you get stuck, there is a botanical difference between thorns and spines. Thorns are modified branches made of the same substance as the branch from which they grow. Many plants have thorns–trees such as the palo verde, shrubs such as the cat’s claw, and even wildflowers such as the prickly poppy have thorns.

Spines on the other hand are modified leaves. They are formed of different material from the stems out of which they grow. The best example of this modification is the cactus. A cactus stem is soft and succulent because it stores water. The stem is green because it contains the chlorophyll that enables the plant to photosynthesize food. The spines which grow from the cactus stem are hard and solid. The spines grow from the base in the same way that leaves grow. However, unlike normal leaves, spines are saturated with calcium carbonate and pectin to make them stiff and hard. They contain no chlorophyll for food production, but they are extremely important to the plant in several other ways.

Spines play a major role in producing the micro climate a cactus needs to survive. All plants have specialized means of working with the environment in which they grow to adjust that environment for survival and reproduction. In many plants, the leaves provide temperature-reducing shade that enables the roots to continue functioning. Other desert plants such as saltgrass, mesquite, and ocotillo reduce overall exposure to the sun by folding or dropping their leaves. Cactus evolved a different adaptation, converting their leaves to tough spines which won’t burn or wither and help shade the stem from the sun. The spines of such cactus species as the fishhook or pincushion cactus, (mammillaria species), or the Rainbow Hedgehog, (Echinocereus rigidissimus), overlap and completely cover the stem. Cactus spines of all species complement the ribbed or noded shape of the cactus stem to produce shade which reduces moisture loss from the stem. The spines, ribs, and round shape of the cactus combine to make sure that no single part of the cactus receives the brunt of the hot sun all day long.

Spines of a cactus species growing in full sun are often longer or denser than spines of that same species growing where shaded by canyon walls or rocks. The shade that the spines help produce is important to the survival of the plant. Without the shading of the spines the stem would lose moisture too rapidly and scorch or burn in the hot sun. Home gardeners sometimes make the mistake of placing a cactus grown in a shaded nursery in a sunny west window where it burns and dies within a few days. A cactus brought from a nursery needs time to adjust to full outdoor sun.

It seems obvious to us humans that spines also protect the succulent cactus stems from being eaten by animals. However, packrats and other rodents feast on cholla cactus while peccaries, javelina, rabbits, and cattle eat both pads and fruit of prickly pear type cacti. In fact, there are many examples of animals using the spines of cactus to their own advantage. Rodents and birds climb and perch amid the spines of all types of cactus. The cactus wren nests almost exclusively in cholla. Packrats use cholla joints to cover their nest mounds. Loggerhead Shrikes impale lizards on saguaro spines. No doubt cactus spines are a deterrent to some animals, but perhaps the protective role of spines is a human emphasis based on our experience. The spines certainly make us wary.

While visiting the Anza-Borrego Desert Museum, I saw a little girl about four years old, walk up to a blooming cholla and bend her head over to smell the yellow flowers. Immediately I heard her scream. A cholla joint had stuck on her face, covering her eye. She screamed and her mother panicked at the sight of the spines stuck on eyebrow, eyelid, and cheek. The paramedics had to be called to remove the spines. The little girl will probably always remember the “protectiveness” of the cholla.

The cholla spines that attached the cactus joint on the girl’s face were not involved in protection, but in reproduction. Cholla are opuntia cactus. Opuntia have sections–joints or pads–which break off and root to form new plants. Many opuntia spines are barbed on the end. These barbs embed in the flesh or hair of a passing animal and dislodge the joint. The central hooked spines of fishhook cacti are also designed to hook into the flesh of an animal passing by and drag the entire plant to a new location where it can develop new roots. If the roots are alive and strong, the fishhook breaks and the plant stays put. If the roots are dead, the fishhook holds and pulls up the plant. Cactus roots and lower stems can dry up and die during times of extreme drought. The stems to parts remain viable for a long time and can produce new roots. The hooked spines of the mammillaria and the barbed spines of the opuntia help the viable top part of the stems transplant to new soil.

First Aid for Spines

Some spines seem to hurt more than other ones, leading to the opinion that some cactus are poisonous. There are no cactus spines which are poisonous. The hurt that some spines, such as the cholla, cause are due to barbs on the ends of the spines. The barbs affect more nerve endings in more tissue than a simple spine or thorn would thus causing more pain. Cholla cacti often have a rough sheath covering their spines. This sheath also damages tissue as it enters the flesh and adheres to the flesh when it is removed. It seems that the spines will rip the skin off when they are pulled out. Some people feel intense pain for hours after removing the spines.

The standard first aid for cholla joint removal is the comb method. Insert the teeth of a comb between the cholla joint and the skin. Leave enough of the comb exposed so that you can grip it. Holding the exposed portion of the comb, flip the cactus joint away from the body. Be careful not to flip the cactus on another person. Also, be careful to hold your own face well away from the joint as you flip it. Even for those of us who don’t have much other use for it, a long, strong comb should be standard equipment on a desert trip.

Another useful item for spine first aid is a lightweight pocket tool with pliers and tweezers. These can be used to grip embedded spines broken off from the cactus. Opuntia also have very tiny hair-like spines called glochids. These embed quickly in almost any contact with the plant. They are difficult to see and are annoying but usually not painful. Glochids can be removed with tweezers or by adhering a piece of duct tape over the spines and then pulling it off. They can be broken off by rubbing. The tiny part that stays in the skin is absorbed without harm.

The spiny adaptations of plants are part of the miracle of life in the desert. Our contact with them can sometimes be painful, but I love the desert, not in spite of, but because of all the things there that poke and stick.