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Spines give cacti a very distinctive appearance. Many plants have thorns or spines, but they may be more characteristic of cacti than of any other plant family. Spines come in a wide range of forms, shapes, and colors, and they perform many protective functions. Although the cactus grower may appreciate spines from a functional and aesthetic point, they also can make working with the plants difficult. However, there are some tools and techniques to make the process less painful.
(Editor's Note: This article was originally published on May 28, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
Spines appear to be similar to thorns, but structurally they are different. Cactus spines are widely considered to be modified leaves, where thorns are extensions of the branch structure.
Spines serve many purposes, most of them protective.
Spines protect a plant from the weather. They can provide shade and slow down the drying winds. In cold climates, they may allow the insulating snow or leaves to stick better around the plant. Very broadly speaking, the few spines a species has, the more benign the climate. Cholla cactuses (Cylindropuntia species) from the American deserts are a mass of spines. Cacti from the rainy tropics, like the orchid cactuses (Epiphyllum species), have nearly no spines at all.
In regions where rain is scarce but fog is common, dew can collect on spines and drip to the ground in the plant's root zone.
Spines can aid in a plant's reproduction. Some cholla cactuses produce little or no seed. Their joints are so loosely attached to the plant that they almost seem to jump out at a passerby and thus some are called "jumping cholla". Even the most delicate brush against the plant can dislodge the joints. They also attach themselves to desert animals, who spread the joints to new area where they may root and grow new plants.
Cactus spines can catch and hold debris from other plants. I have never read any expert opinion on this, but it appears to me that the debris may help to shade or shelter the cactus from the wind and the decomposing debris can enrich the soil.
Spines come in a variety of shapes, colors, and forms. They can even be found in a variety of shapes, colors, and forms on the same plant. They can be sparse or dense, straight or fishhook, long or short, stiff or hairlike, and on and on. Some species have more than one form or shape on a plant. Colors can be white, grey, black, brown, yellow, pink, and just about anything except green or blue. The following photos show a sampling of the variety found in cactus spines.
Tephrocactus articulatus var. papyracanthus
The opuntias have special small spines called glochids. These are very easily dislodged from the plant and easily lodge themselves into one's skin where they can be highly irritating. In fact, itching powder was made using glochids. Glochids are so effective that some opuntias have only glochids and no conventional spines. With some opuntias and close relatives, on immature pads or joints, the glochids and spines are encased in a deciduous leaf. Fruits of many species also have spines or glochids.
Glochids on an opuntia
Opuntia basilaris has no spines but has many tiny glochids
Opuntia fruits with glochids
Leaves on young opuntia pads
Handle with Care
Spines make cacti cumbersome to re-pot or transplant, but here are some helpful tips. For smaller plants, I like to use tongs. For larger plants, I fold up several sheets of newspaper in the long direction to form a strap that can be wrapped around the plant. Strips of carpet can be used in the same way. When handling opuntias, do not touch them while wearing leather gloves. The glochids get embedded in the leather and make the gloves unpleasant to use in the future.
Even with the utmost care, if you handle cacti enough, you will eventually get spines or glochids stuck in your skin. I think the best thing for getting out spines is a set of magnifying tweezers, like the one shown in the photo. It is very helpful to have good lighting while you work. Another method that works for some people is to cover the offending spot with a piece of tape and then peel it off. The tape needs to be more sticky than household transparent tape. Some claim that if you cover the spot with white glue, let the glue dry completely, and then peel it off, the spine will come with it. If you get a multitude of fine glochids stuck in your skin, it can be next to impossible to find them all and pull them out. I have found that in situations like this, the glochids can be softened with hand lotion to the extent that they no longer irritate and in a day they'll be gone. An exfoliating skin care product may also help. When all else fails and I can't get a spine or glochid out, I cover it with a bandage so that it is less likely to be rubbed or pressed on and that makes it less irritating. In a day or so I try again to get it out. Note: This is not professional medical advice. Seek professional help as necessary.
The one word that can be attributed to cactus spines is variety. They serve a variety of purposes. They come in a very wide variety of shapes, colors, and forms. Be careful working around spines, but also enjoy them as interesting and sometimes attractive features.