In Praise of Cactus
Not everyone loves cactus. In fact, when some people complain about desert plants, their first words are something to the effect of, “All those cactus are so spiky and ugly!” Well, you know they think they’re talking about cacti, but they’re also including agaves and yuccas, which aren’t anywhere close to the same thing, but they can have serious thorns.
On the other hand, jungle cacti like Christmas cactus, which are indeed true cacti, they don’t have spines at all! I just learned that maybe half the world’s cacti live in the low light of tropical rainforests. More than likely, they wouldn’t survive our dryer, brighter conditions.
A small number of species arrived in Africa and Asia, probably carried by birds, but they came from this side of the globe. All cacti are native to the western hemisphere. So many of them are at home here in the great American Southwest, that it’s hard to picture the desert without them!
People who aren’t familiar with this part of the world might only think of saguaro when they hear about cactus. Those tall stately specimens are emblems of the Sonora desert to our south. Saguaro don’t generally thrive in this area. It’s too cold in the winter. Our summer’s just fine, but when we get a cold snap, they often don’t make it unless they are protected with something like an overcoat.
Cacti are succulent, and almost drought proof, but they don’t live only in hot deserts. Some of them survive in places as northerly as Western Canada, or up in the Andes Mountains, or as far south as Patagonia. These plants are probably the epitome of survival.
One feature they all share - the hard work of photosynthesis gets done by the cactus equivalent of stems and trunks, not leaves.
Prickly Pear cactus
The next time you look at a barrel cactus, or a tall columnar one, try thinking of it as a tree trunk. Of course, this tree trunk has no limbs, just a lot of spiny armament.
If you were to look at one of the many prickly pears (that’s the genus Opuntia), you might think it has nothing in common with other, more normal trees or shrubs. Surprisingly enough, most cacti, perhaps all of them, are very much like normal trees or shrubs.
Let’s take prickly pear. Every one of those green pads (technically called a cladode) is a branch, flattened, for sure, but a branch. They’re all attached to a stem, a center, rooted area, like other shrubs.
The spines we dread are the remains of leaves. They’ve evolved so they don’t lose water or photosynthesize, or much of anything except protection. Very effective protection.
In fact, many prickly pears and chollas have not one, but two lines of defense. The first is the obvious set of spines, which can puncture skin. They’re not necessarily the worst weapons, though. Anyone who’s lightly grazed their hand on a cactus pad has probably discovered the terrible glochids. Some Opuntias have only glochids. These are their numerous, colorless, tiny, second set of spines. They have hooks, which makes them really awful to remove, but you have to get them out.
Mojave cacti are perfectly suited for this environment. Remember - we get about four inches of rain in an average year. We haven’t had an average year in some time. According to the National Weather Service, our total rainfall in all of 2014 was 1.8”. It’s easy to see why drought tolerance is a real plus for survival.
In order to survive dry periods, those plump stems and barrels are full of fluid. When they need to use that fluid, the stems and trunks become progressively thinner. Barrel cacti develop an accordion shape. Even this is another survival tactic. The folds reduce the amount of direct sunlight hitting the plant surface; cuts down on water loss.
Frightening they may be, but cacti deserve admiration and a place in our gardens. In the back, away from paths, pets, and people.
For KNPR’s Desert Bloom, this is Dr. Angela O’Callaghan of the University of Nevada Cooperative Extension.