Why Do Desert Plants Look That Way?

May 3, 2013

Saguaro National Park in Arizona. (Photo credit: Hugh Mason, via Wikipedia)

What is a Ferocactus?

Why do cactus plants sometimes have both flowers and thorns and, during the immense summer heat, why do some drop their leaves and branches while others retain water?

And why do weeds seem, at times, to grow annoyingly in abundance?

"One man's weed is another man's glory," said Jim Malusa, a principal research specialist in the UA School of Natural Resources and the Environment.

The Sonoran Desert seems, at times, full of contradictions. It is marked by a season of tremendous heat during which nightfall can result in freezing temperatures, wildly variant landscapes and thorny, spiny plants that live near others that produce gentle flowers and succulent fruits.

Do you wonder why? Malusa has the answers.

"There are desert plants that are long lived because they spend much of the time dozing," he said. “They're not growing, not reproducing – they're simply waiting for better times."

But Malusa does not want to give up all the answers. There is a course for that.

Malusa is offering Ecology 414/514, "Plants of the Desert," during the UA's Summer Session II, and the class is open to undergraduate and graduate students.

The course serves as a general introduction to plant ecology with a focus on desert regions in the southwest, specifically the Sonoran, Mojave or Chihuahuan deserts.

In the course, students learn about vegetative and flower structure, invasive species, plant adaptations, plant physiology and the use of desert plants for culinary and medicinal purposes, among other things. Also, while learning about plant classification, students will produce a plant collection of their choosing.

"You can learn some plants by heart, but you need to know how to identify them," Malusa said, noting that students also will engage in lectures and field trips, with optional field trips to the Arizona-Sonora Desert Museum and Mount Lemmon.

"The act of collecting and writing allow you to have a closer look," he added.

The course began in 1950 under direction of the late UA professor Robert Hoshaw, who introduced the course on the main campus after it has been taught through the UA Extension.

"Hoshaw brought it to campus because he in fact liked desert plants, despite specializing in algae," said Malusa, who first met Hoshaw while a UA undergraduate in the late 1970s.

Dune buckwheat in the sands near Yuma, Arizona. (Photo credit: Jim Malusa)

So, why should you sign up?

Malusa said the course is not designed for strict botanists, but individuals who are interested in learning about the very environment in which they live. And good news: No prerequisites are required.

So, if you have ever taken a trip up Mount Lemmon and do not understand why the landscape changed drastically within a few hundred feet in elevation or if are curious about why the Sonoran Desert is so distinctive, consider signing up with Malusa.

And FYI: Don't tell Malusa, but a type of Ferocactus is shown below. 

Contact: Jim Malusa at 520-621-6424 or malusa@email.arizona.edu.

The flower of a fishhook barrel cactus, also known as Ferocactus wislizeni. (Photo credit: Susan Lynn Peterson via Wikipedia).